An epidemiological study on the occupational risk caused by exposure to aromatic amines was conducted. The cohort consisted of 1,385 workers of a chemical company in which beta-napthylamine (91598) was manufactured. Each of the workers was given a complete physical examination. The study was conducted over a 22 year period; a follow up study was made on the 1,094 surviving members of the original cohort at the end of 40 years. The incidence rate of bladder cancer among these workers was determined; length of service in the factory, mortality among the workers, and pathological confirmation of bladder cancer were taken as criteria. The worker/years at risk were calculated from dates of employment, death, and diagnosis. Background information on variables such as occupational history, race, alcohol and cigarette smoking habits use of aromatic amines, and their knowledge of this chemical, and history of other jobs with potential for bladder carcinogenesis was obtained. Thirteen confirmed cases of bladder cancer patients were identified. Approximately a 4 fold risk of bladder cancer was evident among all workers in this study; black workers with more than 10 years of employment had a risk ratio of 111:1; the onset of bladder cancer was much earlier for black workers when compared to the general population. The incidence of bladder cancer increased with the duration of employment as evidenced by the incidences of respectively. Cigarette smoking and alcohol habits or prior employment in high risk occupations were without any significant effect. The authors conclude that bladder cancer risk is high among workers exposed to beta-napthylamine.