A study of mortality in workers exposed to polychlorinated biphenyls was conducted. This was a followup to an earlier study of 2567 workers employed in two facilities where PCBs were used to manufacture electrical capacitors (SIC-3629). The facilities were located in New York state and Massachusetts. Sequential exposures included Aroclor-1254 (11097691), Aroclor-1242 (53469219), and Aroclor-1016 (12674112). Results of the initial study were considered inconclusive due to the small number of total deaths, 163, and the relatively short period of observation, which ended January 1, 1976. In an updated study, the period of observation was extended through December 31, 1982, and the cohort contained 2588 workers, 1318 females. Followup identified 132 additional deaths and added 16527 person years to that of the original study. Total mortality and mortality from major causes were lower than expected, except for diseases of the circulatory system which were slightly elevated. Deaths from cancer of the liver, gall bladder, and biliary tract, however, were significantly elevated, with a standardized mortality ratio of 280. Most of these occurred in females employed at the Massachusetts facility. When stratified by length of employment and latency, no apparent pattern of increasing risk with increasing length of employment was seen. The author concludes that the study provides limited information indicating that occupational exposure to PCBs may be associated with an increased risk of death from cancer of the liver, gall bladder, and biliary tract. Limitations are due to misclassifications, deaths from cancer types that are different from those observed in animal studies, and lack of a consistent dose response pattern (length of employment and latency).