Disparities in evaluation of patients with rectal bleeding 40 years and older

BACKGROUND & AIMS

Rectal bleeding is associated with colorectal cancer. We characterized the evaluation of patients aged 40 years and older with rectal bleeding and identified characteristics associated with inadequate evaluation.

METHODS

We conducted a retrospective review of records of outpatient visits that contained reports of rectal bleeding for patients aged 40 years and older (N = 480). We studied whether patient characteristics affected whether or not they received a colonoscopy examination within 90 days of presentation with rectal bleeding. Patient characteristics included demographics; family history of colon cancer and polyps; and histories of screening colonoscopies, physical examinations, referrals to specialists at the index visit, and communication of laboratory results. Data were collected from medical records, and patient income levels were estimated based on Zip codes.

RESULTS

Nearly half of the patients presenting with rectal bleeding received colonoscopies (48.1%); 81.7% received the procedure within 90 days. A history of a colonoscopy examination was more likely to be reported in white patients compared with Hispanic or Asian patients (P = .012 and P = .006, respectively), and in high-income compared with low-income patients (P = .022). A family history was more likely to be documented among patients with private insurance than those with Medicaid or Medicare (P = .004). A rectal examination was performed more often for patients who were white or Asian, male, and with high or middle incomes, compared with those who were black, Hispanic, female, or with low incomes (P = .027). White patients were more likely to have their laboratory results communicated to them than black patients (P = .001).

CONCLUSIONS

Sex, race, ethnicity, patient income, and insurance status were associated with disparities in evaluation of rectal bleeding. There is a need to standardize the evaluation of patients with rectal bleeding.

The impact of cross-cultural interactions on medical students' preparedness to care for diverse patients

PURPOSE

Medical students who graduate from schools with diverse student populations are more likely to rate themselves as prepared to care for diverse patients compared with students who graduate from more homogenous schools. This study aimed to identify the types of cross-cultural interactions associated with students' self-rated preparedness.

METHOD

In 2010, the authors developed and administered a Web-based survey that queried Harvard Medical School students about their voluntary interethnic interactions (studying, socializing), participation in diversity-related extracurricular activities, and self-rated preparedness to care for diverse patients. The authors separated students' responses regarding interethnic interactions and participation in diversity-related extracurricular activities into high and low participation, then determined the association between these responses and those to questions about students' self-rated preparedness to care for diverse patients. They used ANOVA and Z tests of proportion to analyze their data.

RESULTS

Of 724 eligible students, 460 completed the survey (64%). Seventy-five percent (324/433) believed they were prepared to care for patients from backgrounds different from their own. Students who spent >75% of their study time with students from different backgrounds or who participated in a greater number of diversity-related extracurricular activities were more likely to rate themselves as prepared to care for diverse patients overall and to perform seven other skills.

CONCLUSIONS

Voluntary cross-cultural interactions, both studying and socializing, are associated with higher self-rated preparedness to care for patients from diverse backgrounds. Medical schools should continue to support multicultural pursuits to prepare students to become physicians sensitive to the needs of diverse patients.

Barrett's esophagus: endoscopic treatments II

The following on endoscopic treatments of Barrett's esophagus includes commentaries on animal experiments on cryotherapy; indications for cryotherapy, choice of dosimetry, number of sessions, and role in Barrett's esophagus and adenocarcinoma; recent technical developments of RFA technology and long-term effects; the comparative effects of diverse ablation procedures and the rate of recurrence following treatment; and the indications for treatment of dysplasia and the role of radiofrequency ablation.

Using medical students to enhance curricular integration of cross-cultural content

We hypothesized that an interested medical student group would be helpful in reviewing tutorial cases and giving relevant feedback on the curricular integration of cross-cultural content using case triggers in a preclinical gastrointestinal pathophysiology course. Self-selected student leaders (n = 9) reviewed pre-existing problem-based learning tutorial cases (n = 3) with cross-cultural triggers, and provided narrative feedback to course faculty. The cases were modified and used for the entire class in the following 2 years. Participating course students' comments and teaching faculty feedback were also noted. Outcomes were a change in case content, student global evaluations of the course, and self-reported faculty comfort with teaching the cases. All three tutorial cases were reviewed by a separate group of 2-3 students. Major and minor revisions were made to each case based on the student feedback. These cases were used in 2007 and 2008 and were the major change to the course during that time. Overall course evaluation scores improved significantly from 2006 to 2008 (p = 0.000). Tutors (n = 22 in 2007; n = 23 in 2008) expressed relief during tutor meetings that students had reviewed the cases. A general framework for eliciting student feedback on problem-based cases was developed. Student feedback, consisting of self-selected students' case reviews and solicited course and tutor comments, added value to a curricular reform to improve the integration of cross-cultural content into a problem-based learning curriculum. Our study underscores the fundamental link between teachers and students as partners in curricular development.

Exposure to both radiation and chemotherapy increases the risk of Barrett's and multilayered epithelium

The relationship between radiation and/or chemotherapy and the development of Barrett's and/or multilayered epithelium has not been investigated before. We ascertained a group of patients exposed to radiation and/or chemotherapy and an unexposed group to compare the prevalence rates of Barrett's epithelium and multilayered epithelium at the time of endoscopy in these two groups. Barrett's epithelium was found in ten of the 19 (53%) exposed patients, compared to eight of 38 (21%) unexposed subjects (P = 0.02). Six of 19 (32%) exposed patients had multilayered epithelium, compared to four of 38 (11%) unexposed subjects (P = 0.06). Twelve of the 19 exposed patients (63%) had either Barrett's or multilayered epithelium, in contrast to ten of 38 (26%) unexposed subjects (P = 0.01). Those with exposure to both chemotherapy and radiation had a significant increase in the risk for Barrett's and/or multilayered epithelium (P = 0.003). This study suggests a relationship between exposure to a combination of radiation and chemotherapy and the development of Barrett's and/or multilayered epithelium.

Integration of racial, cultural, ethnic, and socioeconomic factors into a gastrointestinal pathophysiology course

BACKGROUND & AIMS

Our study describes a faculty development program to encourage the integration of racial, cultural, ethnic, and socioeconomic factors such as obesity, inability to pay for essential medications, the use of alternative medicine, dietary preferences, and alcoholism in a gastrointestinal pathophysiology course.

METHODS

We designed a 1-hour faculty development session with longitudinal reinforcement of concepts. The session focused on showing the relevance of racial, ethnic, cultural, and socioeconomic factors to gastrointestinal diseases, and encouraged tutors to take an active and pivotal role in discussion of these factors. The study outcome was student responses to course evaluation questions concerning the teaching of cultural and ethnic issues in the course as a whole and by individual tutorials in 2004 (pre-faculty development) and in 2006 to 2008 (post-faculty development).

RESULTS

Between 2004 and 2008, the proportion of students reporting that "Issues of culture and ethnicity as they affect topics in this course were addressed" increased significantly (P = .000). From 2006 to 2008, compared with 2004, there was a significant increase in the number of tutors who "frequently" taught culturally competent care according to 60% or greater of their tutorial students (P = .003). The tutor's age, gender, prior tutor experience, rank, and specialty did not significantly impact results.

CONCLUSIONS

An innovative faculty development session that encourages tutors to discuss racial, cultural, ethnic, and socioeconomic issues relevant to both care of the whole patient and to the pathophysiology of illness is both effective and applicable to other preclinical and clinical courses.

Gastrointestinal manifestations of dermatologic disorders

The skin and the gastrointestinal tract may be affected concurrently by the same diseases. Pathogenetically, these conditions may be primarily dermatologic diseases involving the gastrointestinal (GI) tract or systemic diseases involving the skin, GI tract, and liver simultaneously. The correct diagnosis of such conditions relies on the ability of the gastroenterologist to recognize the underlying dermatologic disorder. The goal of this clinical review article is to increase gastroenterologists' awareness and understanding of some of these conditions. Case vignettes are presented and the relevant literature reviewed for epidermolysis bullosa, mastocytosis, hereditary hemorrhagic telangiectasia, and melanoma. This review focuses on increasing gastroenterologists' ability to recognize, diagnose, comprehend, and manage patients with these dermatologic conditions who have GI manifestations. Advances in molecular genetics that provide insight into the underlying pathophysiology and histopathology of these lesions are highlighted.

A faculty development program to train tutors to be discussion leaders rather than facilitators

PURPOSE

During 2003, 2004, and 2005, the role of 70 tutors was changed from that of facilitator to discussion leader, in a preclinical PBL learning course, Gastrointestinal Pathophysiology, by use of three key business school teaching strategies: questions, summaries, and schematics. The purpose of this study was to learn what difference this new approach made.

METHOD

During each of the three study years, 171 (2003), 167 (2004), and 170 (2005) students were given Likert-scale attitudinal questionnaires to rate whether their tutors encouraged student direction of the tutorials and whether the summaries and closure schematics benefited their learning. Students' overall course evaluations and mean USMLE scores were quantitatively analyzed, pre- and postintervention. A variety of statistical tests were used to assess the statistical significance of means at the confidence level of .05.

RESULTS

In the third year of the program, student ratings indicated that their tutors were significantly better at encouraging student direction of the tutorials than in the first year (P < .05). The students reported that the tutorial made a more important contribution to their learning (P < .05), and the course objectives were better stated (P = .038) and better met (P = .007). Overall satisfaction with the course also improved significantly (P = .006). Part I gastrointestinal system mean scores of the USMLE showed a statistically significant increase in 2005 compared with 2001 or 2002.

CONCLUSIONS

The tutor as a discussion leader who questions, summarizes, and uses schematics to illustrate concepts had a significant and positive impact on learning in tutorials, achieving course objectives, improving overall course satisfaction, and increasing a standardized national exam's mean score.

Multilayered epithelium may be found in patients with Barrett's epithelium and dysplasia or adenocarcinoma

To determine if multilayered epithelium (MLE) is a useful prognostic indicator for a benign natural history of Barrett's epithelium, we evaluated endoscopic biopsies from patients with Barrett's epithelium without and with dysplasia and/or adenocarcinoma and from non-Barrett's controls for the presence of MLE. MLE was found in 6% of non-Barrett's controls, 30% of Barrett's patients with no dysplasia, and 14% of Barrett's patients with dysplasia and/or adenocarcinoma. MLE was significantly associated with shorter lengths of Barrett's epithelium in both Barrett's groups. Three of 5 photodynamic therapy patients were noted to develop MLE after therapy. MLE may be found in patients with dysplasia and/or adenocarcinoma and after photodynamic therapy; its presence is not useful as a prognostic indicator for a more benign course of Barrett's. This study confirms that MLE is significantly associated with shorter lengths of Barrett's epithelium.

Prospective evaluation of multilayered epithelium in Barrett's esophagus

OBJECTIVE

We recently identified a distinctive type of multilayered epithelium in two patients with Barrett's esophagus, which shows morphological characteristics of both squamous and columnar epithelium. This study was performed to prospectively evaluate the prevalence of multilayered epithelium in patients with Barrett's esophagus.

METHODS

Mucosal biopsies were obtained from the squamocolumnar junction (Z-line) of 58 patients with endoscopic evidence of esophageal columnar epithelium and from the gastroesophageal junction in 21 patients without endoscopic evidence of esophageal columnar epithelium. Specimens were evaluated for the presence of multilayered epithelium and goblet cells.

RESULTS

Twenty-four of 58 (41%) of the patients with endoscopic evidence of esophageal columnar epithelium had multilayered epithelium compared with only one of 21 patients (5%) in the control group (p = 0.005). Of the 58 patients in the study group, 43 had goblet cell metaplasia and 15 did not (p < 0.001). Only patients with goblet cell metaplasia had multilayered epithelium. Shorter lengths of columnar epithelium were noted in the 24 patients with goblet cells and multilayered epithelium compared with the 19 patients with goblet cells and no multilayered epithelium (p < 0.05).

CONCLUSIONS

Multilayered epithelium is strongly associated with goblet cell metaplasia in patients with endoscopic evidence of esophageal columnar epithelium. These data support the hypothesis that multilayered epithelium may represent a transitional stage in the development of Barrett's esophagus.

Factors that influence the decision to do an adequate evaluation of a patient with a positive stool for occult blood

OBJECTIVE

The factors that influence the decision to do an adequate evaluation for a positive test for fecal occult blood in a middle-aged or elderly patient are largely unknown. Our study was undertaken to determine whether factors such as the number of positive Hemoccult II card windows, age, gender, family history of colon cancer, the patient's concern that he or she might have colon cancer, or history of rectal bleeding influence the evaluation performed.

METHOD

A mass screening program for colon cancer was performed using unrehydrated Hemoccult II cards in the Boston area.

RESULTS

Among the 23,593 Hemoccult II cards returned to Beth Israel Deaconess Medical Center, cards from 1,112 patients (4.7%) were found to be positive for one or more of the six possible card windows. Ninety percent, or 940 patients, over 40 yr of age had follow-up information available. As the number of positive windows increased from one to four, there was a significant trend (p < 0.001) for the adequacy of the evaluation to increase. Family history (p = 0.044) and a patient's worry that he or she might have colon cancer (p = 0.003) significantly improved a patient's chance for an adequate evaluation.

CONCLUSIONS

Hemoccult testing is not followed by an adequate evaluation in a significant proportion of patients. Our study points out for the first time that the number of positive Hemoccult windows significantly influences the decision-making.

Distribution of cytokeratin markers in Barrett's specialized columnar epithelium

BACKGROUND & AIMS

The cell of origin for Barrett's epithelium is unknown. A multilayered epithelium within Barrett's epithelium has been noted recently. To investigate the hypothesis that this multilayered epithelium may be a transitional stage between squamous and Barrett's epithelium, cytokeratin immunocytochemistry was used to examine normal squamous, Barrett's, and multilayered epithelium.

METHODS

Seventeen endoscopic biopsy specimens taken from the squamo-Barrett's junction of 8 patients with Barrett's epithelium and 3 biopsy specimens from the gastroesophageal junction of 3 patients without Barrett's epithelium were investigated. Antibodies to cytokeratins 4 and 13 were used as markers for squamous differentiation, and antibodies to cytokeratins 8 and 19 were used as markers for glandular differentiation. Coded samples were evaluated by immunocytochemistry.

RESULTS

In patients with Barrett's epithelium and control patients, staining with columnar markers was confined to either the Barrett's or the gastric columnar epithelium. Staining with squamous markers was confined to the adjacent squamous epithelium. In contrast, focal areas of multilayered epithelium amidst Barrett's epithelium stained with cytokeratin antibodies for both squamous and columnar epithelium.

CONCLUSIONS

A focal multilayered epithelium within Barrett's epithelium that expresses concurrently both squamous and glandular cytokeratin markers is described. These findings suggest a multipotential cell as the cell of origin of Barrett's epithelium.

Morphological characterization of the squamocolumnar junction of the esophagus in patients with and without Barrett's epithelium

Barrett's esophagus is a metaplastic condition in which the normal stratified squamous epithelium of the distal esophagus is replaced by columnar epithelium. Our group has previously characterized a unique surface cell (the "distinctive cell") at the junction of squamous and Barrett's epithelium. This cell is notable for the simultaneous presence on its surface of both squamous and columnar cell features. The aims of our present study were, first, to evaluate prospectively the frequency with which Barrett's patients have the distinctive cell at the squamo-Barrett's junction; second, to further elucidate the characteristics of the distinctive cell; and third, to perform a combined morphological study of the squamo-Barrett's junction using scanning electron microscopy followed by transmission and light microscopy. We divided study patients into two groups: Group I consisted of Barrett's patients and group II of non-Barrett's control patients. Of eight group I Barrett's patients with junctional biopsies, three were noted to have the distinctive cell (37.5%). In contrast, this cell was not observed in any of the group II control patients. Biopsies in control patients as well as Barrett's patients without the distinctive cell revealed abrupt squamogastric or squamo-Barrett's junctions by scanning electron microscopy and light microscopy. In contrast, biopsies from the Barrett's patients with the distinctive cell revealed junctions that were not abrupt and had the distinctive cells overlying normal squamous epithelium. By scanning electron microscopy, the distinctive cells were flattened, polygonal cells with surface microvilli (a columnar cell feature) and were demarcated from one another by shallow depressions, or by intercellular ridges (a squamous cell feature). By transmission electron microscopy, the distinctive cells were cuboidal in shape with abundant apical microvilli and secretory vesicles. We have confirmed that distinctive cells are present in some Barrett's patients. This cell is a morphologic hybrid, sharing features of both squamous and columnar cells, and may be analogous to hybrid cells identified in other locations that undergo metaplasia (eg, the human cervix). Its origin may be the result of transformation of multipotential basal cells of squamous epithelial origin. We hypothesize that the distinctive cells may represent an intermediate stage in the development of Barrett's epithelium.

Scanning electron microscopy of the human esophagus: application to Barrett's esophagus, a precancerous lesion

In Barrett's esophagus, metaplastic columnar epithelium replaces the normal squamous epithelium. The importance of this lesion lies in the increased incidence of adenocarcinoma of the esophagus occurring in patients with Barrett's esophagus. We characterized the surface epithelial cells of Barrett's esophagus using quantitative scanning electron microscopy. Three distinct surface cell types, in addition to the globlet cell, were recognized in Barrett's epithelium: the gastric-like cell and the intestinal-like cell, both of which were similar to normal gastric and small intestinal surface cells, respectively, by quantitative scanning electron microscopy, and the variant cell which had a range of surface features. In four biopsy specimens from the squamo-Barrett's junction in three patients, we found the distinctive cell that had features intermediate between those of squamous and columnar epithelium. On the distinctive cell's surface there are two disparate structures not normally present on the same cell in the gastrointestinal tract: microvilli (a scanning electron microscopy feature of glandular epithelium) and intercellular ridges (a scanning electron microscopy feature of squamous epithelium). The surface characteristics of this cell were almost identical to those of cells found in the transformation zone of the uterine cervix, an area in which squamous epithelium physiologically replaces columnar epithelium. Scanning electron microscopy of Barrett's esophagus has increased our understanding of this precancerous lesion by showing striking cellular heterogeneity. It has also identified the distinctive cell which may represent an intermediate step in the development of Barrett's epithelium during which the surface characteristics of two different cell types, columnar and squamous, coexist in the same cell.

Detection by scanning electron microscopy of a distinctive esophageal surface cell at the junction of squamous and Barrett's epithelium

Metaplastic columnar epithelium replaces the normal squamous epithelium in Barrett's esophagus. We characterized the surface epithelial cells of the junction between squamous and Barrett's epithelium using scanning electron microscopy and light microscopy. In four biopsy specimens from the squamous-Barrett's junction in three patients, we found a distinctive cell type having features intermediate between those of squamous and columnar epithelium. Its distinguishing characteristic is the presence on its surface of two disparate structures not normally present on the same cell in the gastrointestinal tract: microvilli (a scanning electron microscopy feature of glandular epithelium) and intercellular ridges (a scanning electron microscopy feature of squamous mucosa). The surface characteristics of this newly recognized cell were strikingly similar to those of cells found in the transformation zone of the uterine cervix, an area in which squamous epithelium physiologically replaces columnar epithelium. We also examined 28 biopsies of the gastroesophageal junction area from 14 patients with and without a history of heartburn but with no evidence of Barrett's esophagus. None of these biopsies showed the distinctive cell. We hypothesize that this distinctive cell represents an intermediate step in either the development or the healing of Barrett's epithelium, during which surface characteristics of two different cell types, columnar and squamous, coexist on the same cell.

Light microscopic immunocytochemical localization of hepatic and intestinal types of fatty acid-binding proteins in rat small intestine

Monospecific antisera to purified hepatic fatty acid-binding protein (hFABP) and gut fatty acid-binding protein (gFABP) have been used to localize these two proteins in the small intestine of fed rats at the light microscopic level. Pieces of duodenum, jejunum, and ileum were removed from 4-, 10-, 20-, 22-, and 60-day-old Sprague-Dawley rats. Both cryostat and paraffin sections were studied for the presence of hFABP or gFABP by the avidin-biotin immunoperoxidase method. Slides were graded blind for the intensity of staining. Despite the structural and immunological differences between these two proteins, we showed no major differences between their staining patterns or their staining intensity throughout the intestine during postnatal development. The staining for both fatty acid-binding proteins was cytoplasmic. No brush border staining was found. Staining was more intense in the proximal rather than distal intestine, in the villus rather than crypt cells, and in the apex rather than the base of intestinal cells. Shifts in staining patterns, and staining intensity occurring during development may be related to variations in dietary fat intake, rates of cell proliferation, intestinal anatomy, and mechanisms for fat absorption.

Scanning electron microscopic appearance of chronic ulcerative colitis with and without dysplasia

This study was conducted to determine whether scanning electron microscopy of colonic mucosal biopsy specimens can help to detect dysplasia in patients with chronic ulcerative colitis. In the first phase of the study, using light microscopy as the standard for the diagnosis, the scanning electron microscopic appearance of specimens from patients with chronic ulcerative colitis and control patients was examined. Descriptive criteria were established to identify normal, atrophic, and dysplastic colonic mucosa. In the second phase, quantitative techniques were used to develop more objective criteria for the diagnosis of dysplasia in ulcerative colitis. Twenty-one coded colonic specimens from 11 patients were sequentially examined by scanning electron microscopy and by light microscopy. The three morphometric analyses performed on the surface epithelial cells were number of cells per unit area, number of microvilli per unit area, and percentage of microvilli with a normal width. The cell count and percentage of microvilli with a normal width were significantly reduced in the seven specimens with colonic dysplasia as compared with non-dysplastic tissues. Scanning electron microscopy may serve as an adjunct to light microscopy in the diagnosis of colonic dysplasia.

Distribution of immunoreactive alkaline phosphatase in the adult rat ileum by immunoperoxidase staining at the light microscopic level

Our prior immunocytochemical studies using monospecific antibody to alkaline phosphatase, Bouin's fixation, and paraffin sections demonstrated a decreasing gradient of villus brush border staining from the proximal to the distal rat small intestine. In addition, we noted an unusual pattern of staining in the terminal centimeter of the adult rat ileum: the villus brush border staining was less intense than crypt brush border staining. To determine whether this pattern of staining was present throughout the entire ileum, we examined alkaline phosphatase staining in two separate jejunal sites and the entire lowest third of the intestine of adult Wistar rats. With Bouin's fixation and paraffin embedding, both conventional and germ-free rats showed the same unusual staining pattern throughout the entire ileum. This pattern suggested that bacterial proteases were not responsible for the diminished ileal brush border alkaline phosphatase. However, when acetone fixation and cryostat sections were used with the avidin-biotin-peroxidase complex system, the previously noted reversed gradient of staining between the ileal villus and crypt areas was no longer present. Rather, ileal crypt brush border staining was less than ileal villus brush border staining. With either methodology, jejunal villus brush border staining was significantly more intense than ileal brush border staining, whereas the deep crypt brush border staining was not significantly different between the two regions. The present study reinforces the need for a combination of methodologies in order to best and most accurately localize certain antigens with immunocytochemistry. It also confirms a decreasing proximal to distal gradient for villus brush border alkaline phosphatase despite similar deep crypt brush border staining throughout the small intestine.

Esophageal dysplasia. Assessment by light microscopy and scanning electron microscopy

This study was performed to determine the characteristics of esophageal dysplasia by scanning electron microscopy. A total of 82 esophageal biopsy specimens were taken from 30 patients who were divided into three groups. Group 1 patients had no known esophageal disease. Group 2 patients had squamous cell cancer. Group 3 patients had esophagitis. Mucosal biopsy specimens that had been diagnosed by light microscopy as normal, esophagitis, or dysplastic mucosa were examined by scanning electron microscopy. A characteristic appearance for each type of mucosa was recognized by scanning electron microscopy. A quantitative analysis of the scanning electron microscopy feature of microridge density showed a statistically significant difference not only between normal and dysplastic mucosa, but also between esophagitis and dysplastic mucosa. The addition of scanning electron microscopy to light microscopy may prove helpful in the diagnosis of dysplasia as well as in the understanding of the biologic behavior of dysplastic cells and possibly their relationship to esophageal carcinoma.

The identification and management of patients with a high risk for cardiac arrhythmias during modified ECT

The authors describe the cardiovascular complications of ECT in 42 patients undergoing this procedure during a one year period at a psychiatric referral center. Twenty-eight percent of the entire group of patients developed ischemic and/or arrhythmic complications following ECT. Seventy percent of the patients who had a history, physical or EKG evidence of cardiac disease developed cardiac complications. On the basis of this data, a high risk category for ECT is defined more precisely than previously. Recommendations are made for managing this high risk category of depressed patients in order to treat them with maximum safety and effectiveness.

Localization of immunoreactive alkaline phosphatase in the rat small intestine at the light microscopic level by immunocytochemistry

Monospecific antibody to purified alkaline phosphatase hs been used to localize alkaline phosphatase in the rat small intestine at the light microscopic level. Pieces of duodenum, jejunum, and ileum were removed from 2-, 9-, 12-, 18-, 21-, 26-day-old and adult wistar rats. They were fixed in Bouin's fluid and examined for the presence of alkaline phosphatase by th immunoperoxidase method. Slides were graded blindly for the intensity of staining. The localization of alkaline phosphatase by the immunoperoxidase method extends previous histochemical observations in several ways. First, diffuse cytoplasmic staining is present particularly in the opical portion of the villus and crypt epithelium. Second, staining for alkaline phosphatase is present on the brush border and in the apical portion of the deep crypt cells throughout the duodenum, jejunum, and ileum at the various ages tested. Third, in the adult rat distal ileum there is more staining on the brush border of the deep crypt epithelial cells than on the villus absorptive cells. These observations are consistent with the presence of a non-brush border alkaline phosphatase in all intestinal cells and with fan enzymatically inactive form of alkaline phosphatase in the deep crypt epithelium.