All ascertainable cases of malignant mesothelioma in Australia were notified to a national surveillance program in the period January 1, 1980 to December 31, 1985. There were 854 cases obtained and 823 confirmed on clinical (77) or histologic (746) ground. Tumor site was known in 759 cases (685 pleural and 74 peritoneal). Lung fiber content analyses by light microscopy and analytic transmission electron microscopy with energy-dispersive x-ray analysis were done on 226 cases in which postmortem material was available, using the method of Rogers. Cell type was determined by a five-member expert panel of pathologists appointed by the Royal College of Pathologists of Australasia. There was a statistically significant trend between lung fiber content (fibers/g dry lung) and cell type from epithelial (low fiber content) through mixed to sarcomatous (high fiber content). This trend was most apparent for total uncoated fibers (chi-square = 6.8, df = 1, P less than 0.01) and crocidolite (chi-square = 6.7, df = 1, P less than 0.01). Lung fiber content also was associated with tumor site; higher lung fiber content being associated with peritoneal tumors. This relationship was significant for all fiber content measures except chrysotile and was independent of the fiber content-cell type relationship (log-linear analysis). Survival from time of provisional diagnosis was significantly longer for epithelial (mean, 13 months; standard deviation [SD], 12.8) and mixed (mean, 10.2 months; SD, 8.7) types than sarcomatous cell types (mean, 5.8 months; SD, 6.5; P less than 0.0001, by analysis of variance on log10 survival time). Survival time was significantly greater for pleural tumors (mean, 11.4 months; SD, 13.4) than peritoneal tumors (mean, 8.6 months; SD, 12.5) (P less than 0.005, by Student's t test on log10 survival time).