The advancement of a new human factors report--'The Unique Report'--facilitating flight crew auditing of performance/operations as part of an airline's safety management system

This paper presents the findings of research relating to the specification of a new human factors report, conducted as part of the work requirements for the Human Integration into the Lifecycle of Aviation Systems project, sponsored by the European Commission. Specifically, it describes the proposed concept for a unique report, which will form the basis for all operational and safety reports completed by flight crew. This includes all mandatory and optional reports. Critically, this form is central to the advancement of improved processes and technology tools, supporting airline performance management, safety management, organisational learning and knowledge integration/information-sharing activities. Specifically, this paper describes the background to the development of this reporting form, the logic and contents of this form and how reporting data will be made use of by airline personnel. This includes a description of the proposed intelligent planning process and the associated intelligent flight plan concept, which makes use of airline operational and safety analyses information. Primarily, this new reporting form has been developed in collaboration with a major Spanish airline. In addition, it has involved research with five other airlines. Overall, this has involved extensive field research, collaborative prototyping and evaluation of new reports/flight plan concepts and a number of evaluation activities. Participants have included both operational and management personnel, across different airline flight operations processes. Statement of Relevance: This paper presents the development of a reporting concept outlined through field research and collaborative prototyping within an airline. The resulting reporting function, embedded in the journey log compiled at the end of each flight, aims at enabling employees to audit the operations of the company they work for.

Treatment of fallopian tube carcinoma with cyclophosphamide, adriamycin, and cisplatin

Primary carcinoma of the fallopian tube is uncommon; optimal primary treatment is still not well defined, and little information is available about the efficacy of cisplatin-based combination chemotherapy. Thirty-eight patients with fallopian tube carcinoma were treated with cyclophosphamide (500 mg/m2), Adriamycin (50 mg/m2), and cisplatin (50 mg/m2) (CAP). Thirty-two patients received the combination chemotherapy as first-line treatment after cytoreductive surgery, whereas six subjects were treated for recurrent disease. The patients received a median of six cycles of therapy (range, four to nine). At the initiation of chemotherapy, 24 patients had measurable lesions. In this group of patients, 15 had a clinical complete response (CR), four had a partial response (PR), three had stable disease (SD), and two had progressive disease (PD) after chemotherapy. The overall clinical response rate (CR + PR) was 80%. Ten of the 14 CR patients who were submitted to second-look operation (SLO) were found free of disease, in pathologic complete response (pCR). Three pCR patients relapsed, and two of them died despite second-line treatment. Nine patients achieving PR, SD, and PD after first-line chemotherapy were further treated (five with chemotherapy, two with radiotherapy, two with progesteron), but none responded to second-line treatment and all died (median survival, 9 months). Fourteen patients without gross residual disease after cytoreductive surgery had no measurable lesions and were not evaluable for response. Seven of them had negative SLO and remain disease free. Three patients (two stage III and one stage II) who refused SLO relapsed 14, 16, and 26 months after completion of chemotherapy. The median survival for the entire group was 38 months, and the 5-year survival rate was 35%. The toxicity of the regimen was moderate. The CAP regimen appears to be active in primary fallopian tube carcinoma and yields response rates comparable to those reported for epithelial ovarian cancer.

Endometrial stromal sarcoma: analysis of treatment failures and survival

The objective of this retrospective multicenter study was to assess the rates, times, and sites of recurrences of 26 patients with low-grade endometrial stromal sarcomas (ESS) (<10 mitoses per 10 high-power fields (HPF) and 40 patients with high-grade ESS (>10 mitoses/10 HPF). Surgery was the initial therapy for all patients. Postoperative treatment was given without well-defined protocols. The median follow-up of survivors was 92 months (range, 4-167). Low-grade ESS: Of the 20 patients with disease confined to the uterus, 5 (25.0%) developed pelvic recurrence after a median of 36 months (range, 4-108). Of the 6 patients with disease outside the uterus, only one recurred in the pelvis after 93 months. High-grade ESS: Of the 20 patients with disease confined to the uterus, 11 (55.0%) developed recurrent disease after a median of 5 months (range, 2-76). The relapse occurred in the pelvis in 3 patients, in upper abdomen in 3, in upper abdomen and extraabdominal sites in 1, and in the pelvis and upper abdomen or extraabdominal sites in 4. Of the 12 patients with extrauterine disease confined to the pelvis, 9 (75.0%) developed recurrent disease after a median of 12 months (range, 1-49). The relapse occurred in the pelvis in 3 patients, in extraabdominal sites in 3, and in the pelvis and upper abdomen or extraabdominal sites in 3. Of the 8 patients with extrauterine disease outside the pelvis, 7 died of disease and 1 is currently alive with progressive disease after 24 months. The disease-free survival was significantly better for low-grade than that for high-grade ESS (P = 0.0001). By log-rank test the disease-free survival of high-grade ESS patients was related to stage (P = 0.0466) and mitotic count (P = 0.0014), but not to age. Cox model showed that mitotic count was the only independent prognostic variable for high-grade ESS (P = 0.006). In conclusion, low-grade and high-grade ESS have a completely different biological aggressiveness and clinical behavior.

Phase II study of paclitaxel as salvage treatment in advanced endometrial cancer

OBJECTIVE

To evaluate the antitumour activity of paclitaxel in patients with endometrial cancer pretreated with cisplatin, doxorubicin and cyclophosphamide (PAC).

MATERIALS AND METHODS

Eligible patients had complete initial surgery, expected survival > or = 3 months, performance status < or = 1, measurable or evaluable disease. Paclitaxel was given over three hours at the dose of 175 mg/m2, repeated every 3 weeks. Tumour response was first evaluated after 3 cycles. A maximum of 10 cycles was given in responders.

RESULTS

19 patients entered the study and a total of 105 cycles were administered. Complete and partial responses were achieved in 2 and 5 patients, respectively, for an overall response rate of 37% (95% CI: 16%-62%). The response rate in patients refractory to platinum was 22%. One patient is alive without evidence of disease 16 months after the start of treatment. The most common side effects were mild to moderate myalgia and peripheral neuropathy, which occurred in 31% and 47% of patients, respectively. In only 1 patient treatment had to be discontinued because of severe myalgia.

CONCLUSION

Paclitaxel is active in patients with endometrial cancer pretreated with PAC. Further studies with paclitaxel incorporated in the initial treatment for advanced disease are warranted.

Interferon-beta can induce progesterone receptors in human endometrial adenocarcinoma

BACKGROUND

The induction of estrogen and progesterone receptors (ER and PGR) has been reported in breast and endometrial cancer cells exposed to human fibroblast interferon-beta (hIFN-beta). Clinical verification of this finding might provide the rationale for new therapeutic approaches. This study was designed to evaluate whether clinical treatment with high doses of hIFN-beta induced ER and PGR in patients with endometrial adenocarcinoma.

METHODS

Two biopsies were obtained, 1 before and 1 after hIFN-beta treatment (3 x 10(6) i.m. every other day for 3 weeks) from 36 patients with endometrial adenocarcinoma. ER and PGR were determined with standard procedures using radiolabeled ligands.

RESULTS

hIFN-beta treatment did not affect the proportion of ER-positive (i.e., >15 fmol/mg protein) or PGR-positive (i.e., >20 fmol/mg protein) cases. However, in patients with detectable ER and PGR at baseline, hIFN-beta raised the levels. Using a 35% difference before and after therapy as a cut-off, 72 and 79% of cases had increases in ER and PGR, respectively. The difference was highly significant for PGR.

CONCLUSIONS

In patients with endometrial adenocarcinoma with undetectable ER or PGR, hIFN-beta did not induce the expression of these receptors. When the receptors were present they were upregulated by hIFN-beta. Whether this increase in receptor levels, particularly PGR, has therapeutic applications remains to be established.

Brain metastases from endometrial carcinoma

Central nervous system (CNS) involvement by endometrial carcinoma is uncommon. Among 1069 patients registered for endometrial carcinoma at our institution between 1982 and 1994, 10 (0,9%) developed brain metastases. Median age at the time of CNS metastasis diagnosis was 59 years. Median interval between diagnosis of endometrial cancer and documentation of brain involvement was 26 months. Clinical manifestation of brain metastasis included headache (80%), motor weakness (50%), seizures (20%), confusion (10%), balance (10%), and visual disturbances (10%). All lesions (4 multiple, 6 single) were contrast enhancing on computed tomography (CT) scans, and were located in the cerebrum in seven cases, in the cerebellum in one case, and in both in two cases. The CNS was the only site of detectable disease in six patients with recurrent disease. Nine patients died and one is alive with disease 3 months after surgical resection of a single cerebral deposit. Median survival from diagnosis of brain metastases for the entire series was 1 month (range 1-83). Six patients receiving only steroids died within 1 month from the diagnosis. One patient received radiotherapy (survival, 3 months) and two underwent surgical resection of solitary metastasis followed by radiotherapy (survival = 28 and 83 months). Prognosis of patients with CNS metastases from endometrial carcinoma appears poor; however, in a selected group of patients early diagnosis followed by multimodal treatment may result in a palliation of the disease.

Limited invasiveness to assess retroperitoneal spread in stage I-II ovarian carcinoma

OBJECTIVE

To evaluate the incidence of retroperitoneal metastases, survival rate and site of recurrence in early ovarian tumors undergoing limited retroperitoneal surgery.

METHOD

Three hundred seventy-three consecutive patients underwent assessment of the retroperitoneum consisting of intraoperative palpation with or without biopsies.

RESULTS

Retroperitoneal metastases were detected in 10 stage-I tumors (3.2%) and in 10 stage-II tumors (16%). The risk was inversely related to tumor differentiation. Palpation revealed metastases in 10 cases. During follow-up, none of the borderline tumors (1.9% of stage-I grade-1 node-negative, 2.7% of grade-2 and 7.0% of grade-3 tumors) recurred in the retroperitoneum. In stage II, two recurrences were observed in grade-2 tumors (11%) and one in grade 3 (4.5%).

CONCLUSION

Limited retroperitoneal surgery enables satisfactory outcome in early ovarian cancers. Risk of retroperitoneal recurrence is minimal in grade 1 and non-existent in borderline tumors. Less differentiated tumors have low risk but further investigation of the therapeutic role of lymphadenectomy is justified.

In search of specific cytotoxic T lymphocytes infiltrating or accompanying human ovarian carcinoma

Lymphocytes infiltrating human ovarian carcinoma obtained directly from the tumour mass (tumour-infiltrating lymphocytes, TIL) or from the carcinomatous ascites (tumour-associated lymphocytes, TAL) were expanded in vitro in long-term cultures with interleukin-2 and tested for their specific cytolytic activity. Killing of the autologous tumour was detected only in a proportion of the patients, less frequently in TIL compared to TAL. In fact two out of ten TIL and four out of nine TAL cultures tested showed significant levels of lysis against the autologous tumour. This cytotoxic activity was not restricted to the autologous tumour, as other tumour cell lines, including non-ovarian ones, were lysed as well. The cultures that were not cytotoxic against the autologous tumour were in most cases able to lyse other tumour cell lines of ovarian or other histology. Cloning of TIL from one patient was performed: of 22 clones tested, 4 displayed higher cytotoxicity against the autologous tumour compared to the uncloned population and 3 out of these 4 did not kill an irrelevant carcinoma cell line. In order to stimulate the expansion of putative specific effectors we performed mixed lymphocyte/tumour cultures (MLTC) with autologous or allogeneic tumour cells. No stimulation of cytotoxicity against the autologous tumour was detected after MLTC in nine different TAL populations, using autologous or allogeneic tumours as stimulators. On the contrary, peripheral blood lymphocytes from two patients after MLTC with the autologous tumour showed increased killing of the autologous and decreased killing of an allogeneic target. In conclusion TIL and TAL from ovarian carcinoma expanded in vitro with interleukin-2 usually have non-MHC-restricted cytotoxicity and variable degrees of reactivity against the autologous tumour. A preferential killing for the autologous tumour was not observed even after MLTC. These results do not exclude the existence of tumour-specific cytotoxic T lymphocytes in ovarian carcinoma; nevertheless they suggest that putative specific effectors have very low frequency and that culture techniques for expanding their growth more selectively are still to be optimized.

Etiology of severe asthenozoospermia and fertility prognosis. A screening of 5216 semen analyses

A review of n = 5216 semen analyses performed in our two Clinics from January 1986 to December 1989 allowed to identify n = 35 patients whose sperm had constantly very low motility (less than 5% progressive motile gametes in three subsequent analyses; necrozoospermia cases were excluded from this study). This apparently rare but severe anomaly was found to be associated not only with ultrastructural anomalies (n = 18), but also with positive seminal bacteriology (n = 8) or the presence of antisperm antibodies (n = 2). In eight cases the cause(s) for this constant asthenozoospermia remained obscure. The fertility potential of the men affected was followed-up and is discussed in relation to their anamnesis, physical exam and seminal characteristics.

Determination of ectoenzyme activities in leukemic cells and in established hematopoietic cell lines

Ectoenzyme activities were determined in peripheral blood cells from patients with acute leukemias, from normal controls, and in cells of hematopoietic cell lines. In common acute lymphoblastic leukemia, cell membrane-associated 5'-nucleotidase (5'-N) activity was significantly higher than in acute T and unclassified lymphoblastic leukemias. In acute myeloblastic and myelomonocytic leukemias, cells contained significantly higher gamma-glutamyl transpeptidase (gamma-GT) activity than in lymphoblastic leukemias. Normal B lymphocytes differed from T cells and monocytes mainly in their 5'-N activity, whereas in monocytes, gamma-GT activity was more pronounced than in other normal blood cells. Hematopoietic cell lines showed some distinct patterns of ectoenzyme activity. Most B cell lines had high 5'-N and (Na-K-Mg) adenosine triphosphatase activities. In lines of myeloid origin, elevated gamma-GT values were found. In lymphoid stem cells and in T lymphoblast lines, most ectoenzyme activities were lower than in the other cell lines. In some cell lines, characteristic high-activity marker enzymes were detected.

Characterization of acute undifferentiated leukemia by combined analysis of plasma membrane-associated gamma-glutamyltranspeptidase and soluble terminal transferase

gamma-Glutamyltranspeptidase (gamma-GT) is a plasma membrane-associated enzyme present in blasts of certain acute leukemias. We analyzed 90 cases of undifferentiated and differentiated acute leukemias for gamma-GT, using a colorimetric assay. Blasts of all patients with common acute lymphoblastic leukemia (ALL) and T-ALL were negative for gamma-GT (less than 5 units). In contrast, gamma-GT was significantly elevated in acute myeloblastic or monoblastic leukemia blasts (P less than .001). In 16 cases of acute undifferentiated leukemia (AUL) studied, the levels of gamma-GT ranged from 0 to 93 units; in eight cases, gamma-GT was positive (greater than 5 units), and six of these had 2% to 5% Sudan black-positive leukemic cells in the blast-enriched suspension. Combined gamma-GT/TdT analysis revealed that both enzyme markers were mutually exclusive in 75% of AUL cases, suggesting that gamma-GT+/TdT-blasts are of nonlymphoid origin, and gamma-GT-/TdT+ blasts are of lymphoid origin. Two cases were devoid of both enzyme activities and could represent truly undifferentiated leukemia. Thus, combined gamma-GT/TdT analysis underlines the heterogeneity of AUL and appears to be useful in defining the lineage commitment of undifferentiated leukemic blasts.

Detection of the common acute lymphoblastic leukemia antigen in the serum of leukemia patients

The common acute lymphoblastic leukemia antigen (CALLA) has been detected in biological fluids using a radioimmunoassay based on the inhibition of binding of 125I-labeled monoclonal anti-CALLA antibody to glutaraldehyde-fixed NALM-1 cells. With this assay, we showed first that CALLA was released in culture fluids from NALM-1 and Daudi cell lines but was absent from culture fluids from CALLA negative cell lines. Then, we found that the sera of 34 out of 42 patients (81%) with untreated common acute lymphoblastic leukemia (c-ALL) contained higher CALLA levels than any of the 42 serum samples from healthy controls. The specificity of these results was further demonstrated by testing in parallel the sera from 48 patients with CALLA negative leukemias, including 26 acute myeloid leukemia (AML), 12 T-cell acute lymphoblastic leukemia (T-ALL), and 10 acute undifferentiated leukemia (AUL). All of these sera gave negative results, except for one patient with AUL, who had a significantly elevated circulating CALLA level, and one patient with AML, who had a borderline CALLA level, 3 SD over the mean of the normal sera. Preliminary results suggest that circulating CALLA is associated with membrane fragments or vesicles, since the total CALLA antigenic activity was recovered in the pellet of the serum samples centrifuged at 100,000 g. In addition, the CALLA-positive pellets contained an enzyme considered as a membrane marker, 5'-nucleotidase. Evaluation of the clinical importance of repeated serum CALLA determinations for the monitoring of c-ALL patients deserves further investigation.

[Familial myeloproliferative syndrome]

The case histories of three patients with hematologic disorders are reviewed. The patients are members of the same family composed of three brothers and two sisters. Two have osteomyelofibrosis and one essential thrombocythemia. Hematologic, enzymatic, cytogenetic, immunocytologic and immunogenetic investigations allow the following conclusions: - all the 5 siblings have identical blood group and rhesus factor (0+); - there is an HLA identity in the 5 siblings characterized by the alleles: A2, A3, B5, B7 (w4, w6); - the white blood cell alkaline phosphatase is not increased; - no monoclonality can be shown; - the chromosome Ph 1 is absent. In the second (osteomyelofibrosis) and third (essential thrombocythemia) patient an additional chromosome has been found, while the caryotype of the other three siblings, including the first patient with osteomyelofibrosis, is normal.

[A case of metastasizing paraganglioma of the larynx]

The case of a 68-year-old woman who died of a metastasizing paraganglioma of the larynx is reported. The diagnostic problems related with this disease and its relationship with the tumors of the APUD system are particularly discussed.

A quality control study to assess the inter-laboratory variability of routine estrogen and progesterone receptor assays

The steroid hormone receptor laboratories of Bern, Basel, Zürich, Locarno, Lausanne and Geneva have participated in a quality control study to assess potential inter-laboratory variability in results of tests for determination of steroid hormone receptor status in human breast tumor biopsies. Homogeneous breast tumor powders containing low, medium and high concentrations of estrogen receptors (ER) and progesterone receptors (PR) were prepared in Bern and dispatched on solid CO2 to each laboratory within 1 day of preparation. Each laboratory was requested to assay each powder for ER and PR by their usual procedures. The results revealed that the quantitative discrepancies in ER and PR binding values among the participants could be attributed in part to variations in the methods used for measuring cytosol protein content and also to the differences in hormone receptor assay methods. Nevertheless, all of the laboratories were able to identify the samples containing low, medium and high concentrations of ER and PR.

Correlations between enzymatic and immunologic properties of human peripheral blood mononuclear cells. I. Ectoenzymes of normal and immunodeficient peripheral blood mononuclear cells

The activity of plasma membrane marker enzymes which are involved in purine metabolism (5'-nucleotidase, alkaline 5'-nucleotide phosphodiesterase), in active ion transport (Na-K-Mg-adenosine triphosphatase, ouabain-sensitive Na-K-adenosine triphosphatase), in aminoacid transport (gamma-glutamyltranspeptidase), and in basic physiologic functions (alkaline phosphomonoesterase) were assayed in mononuclear cells isolated from peripheral blood of normal donors and of patients with primary immunodeficiency. Irrespective of the clinical classification of the immunodeficiency, the cells of patients were characterized by significantly diminished 5'-nucleotidase and to a certain extent by lower alkaline phosphomonoesterase activities. Average activity levels of other enzymes were similar in cells of patients and controls, but scattering was more pronounced in the first group. Determination of substrate affinity revealed different kinetic properties of 5'-nucleotidase in cells from patients and normal donors; however, the extent of inhibition by beta-glycerophosphate or alpha, beta-adenosine-methylene diphosphate was comparable for both types of cells. The presence of inhibitory compounds in patients' serum was excluded by mixing experiments. When activities of the various plasma-membrane-associated enzymes were compared with each other, significant correlations emerged in normal lymphocytes. Most of these correlations were absent in cell membranes of immunodeficient patients. The findings indicate that the plasma membrane of lymphocytes from patients with immunodeficiency may be characterized by an altered distribution of enzymatic constituents.

[Classification of acute leukemias by surface markers and correlation with the morphological diagnosis. Results of 111 cases]

111 patients with acute leukemia, including 29 children, were classified according to the surface markers and cytochemistry of their blasts. The acute leukemias were separated into two majors groups (lymphoid and non-lymphoid) depending on the presence or absence of specific lymphoid markers. On the basis of these criteria a correlation of 94% with the hematological diagnosis was obtained. Acute lymphoblastic leukemia (ALL) was divisible into three sub-groups: 11 cases expressing T-cell specific markers were classified as T-ALL and 33 cases expressing the common ALL antigen (CALLA) as c-ALL. 18 of the latter expressed an additional marker, DSA (Daudi surface antigen), splitting c-ALL cases in two subgroups. Cytochemistry of the cases lacking specific surface markers (n = 67) served to diagnose 41 acute myeloid leukemia (AML) cases and 8 monoblastic leukemias. The remaining 18 cases could not be classified. The presence of absence of HLD-DR (Ia) antigens served to subdivide AML into two major subgroups. The prognostic significance of these new diagnostic splits is under active study.

Resolution effect on the stereological estimation of surface and volume and its interpretation in terms of fractal dimensions

Estimating surface and volume density of subcellular membrane systems at different magnifications yield different results. As the magnification is increased from x 18,000 to x 130,000 the estimates of surface density of endoplasmic reticulum and inner mitochondrial membranes increase by a factor of 3, whereas that for outer mitochondrial membranes increase only by 20%. The estimate of volume density of endoplasmic reticulum also increases by a factor of 3. No further increase is observed at magnifications above x 130,000 which is therefore called critical magnification. The findings are interpreted on the basis of the concept of fractals proposed by Mandelbrot, and the fractal dimensions of the membrane systems considered are estimated. This can lead to the derivation of resolution correction factors which permit measurements obtained at any magnification to be converted to estimates at critical magnification. These findings may explain, at least in part, the large discrepancy in the estimates of the surface of cytomembranes found in the literature.

Integrated stereological and biochemical studies on hepatocytic membranes. I.V. Heterogeneous distribution of marker enzymes on endoplasmic reticulum membranes in fractions

The purpose of the study was to consider quantitatively the relationships between the surface area of the endoplasmic reticulum (ER) and constituent marker enzyme activities, as they occur in fractions collected from rat liver homogenates. The ER surface area was estimated in five membrane-containing fractions by use of a combined cytochemical-stereological technique (5), while, at the same time, ER marker enzymes were assayed biochemically. Fraction/homogenate recoveries for the ER enzymes averaged 100%, total membrane surface area 98%, and ER surface area 96%. Relative specific activities, which compare the relative amounts of ER marker enzyme activities to the relative ER surface area in the membrane-containing fractions, indicate variable distributions for glucose-6-phosphatase and NADPH cytochrome c reductase, but not for esterase.

Intergrated stereological and biochemical studies of hepatocytic membranes. I. Membrane recoveries in subcellular fractions

Previous attempts to relate the structure and function of hepatocytic membranes have compared biochemical data of fractions to morphological data derived from either intact tissue or fractions. The effects of the original homogenization aside, biochemical recoveries comparing membrane marker enzymes of the homogenate to subsequent fractions suggest a general conservation of activity. A sterological study was undertaken to estimate membrane surface areas in the intact tissue, homogenate, and fractions of the same livers and then to test the comparability of these data with membrane marker enzymes by calculating both morphological and biochemical recoveries. The sterological data were corrected for errors due to section thickness and compression. The average total membrane sufrace area per 1 g of liver was 9.3 m2 in the intact tissue (T), 7.8 m2 in the homogenate (H), and 7.4 m2 in the fractions (F); recoveries for the membrane surface areas thus averaged 96% for the (F/H) and 81% for the (F/T) comparisons. In homogenate and fractions, the differentiability of membranes by morphological criteria was limited to rough- and smooth- surfaced membranes, as well as outer and inner mitochondrial membranes. The recoveries of rough-surfaced membranes were 101% for F/H and 92% for F/T; those of smooth-surface membranes were 89% for F/H and 107% for F/T. For mitochondrial membranes, a recovery of 100% for F/H was obtained, whereas it amounted to only 54% for F/T. With respect to F/H, the membrane recoveries compare well with the marker enzyme recoveries obtained biochemically. The extension of recovery calculations to the intact tissue (F/T) revealed satisfactory conservation of the procedures of homogenization and fractionation; it indicates, however, that a shift of a substantial part of mitochondrial membranes to the pool of unidentifiable smooth membranes may occur on homogenization.

Stereological method for estimating relative membrane surface area in freeze-fracture preparations of subcellular fractions

Microsomal fractions from liver cells are a mixture of vesicles derived from a number of different cellular membranes. These can be differentiated on freeze-fracture preparations by their characteristic density of intramembranous particles. A stereological method is developed which allows the estimation of the relative membrane surface of the various membrane types by using freeze-fracture preparations. The sample is restricted to concave profiles without cast shadow. The numerical frequency distribution of vesicles with respect to particle density is determined. The estimation of relative surface area must consider the effects on sampling of (a) variable size distributions of vesicles and (b) loss of small profiles. Correction coefficients are derived which allow a differential vesicle count to be transformed into an estimate of relative membrane surface.