All cases of malignant mesothelioma (201) and other primary malignant pleural tumors (19) reported to the Connecticut Tumor Registry from 1955 through 1977 were studied in an attempt to identify high-risk jobs, industries and geographic locations and to estimate the risk attributable to asbestos exposure in the workplace. Data were obtained from hospital records, death certificates and city directories for cases, case spouses and a random sample (604) of Connect/cut decedents (1955-1975). Three cases involved histories of work in asbestos products manufacture, but there was no evidence of residential risk in that geographic area. Relative risk (RR) for carpenters and cabinetmakers was 2.25 (p<. 05); for plumbers and pipefitters, 3.87 (p<.05); and for persons "ever employed" in the rubber industry, 5.08 (p<.01). Occupational exposure was indicated in 85% of the cases; attributable risk (A R) was 36%. Risk increased with greater exposure and older age. AR was 81% in men aged 70 to 89 years at diagnosis. Reduction of unnecessary occupational asbestos exposure remains the highest public health priority.