The incidence of brain tumors was investigated in petrochemical workers. Vital status was determined through company records, social security records, and the state bureau of vital statistics for 7595 male workers who had worked in a petrochemical facility between 1941 and 1977. Observed and expected deaths from brain tumors were tabulated through 1979. Death certificates were obtained and classified. Through 1977, 96.7 percent of the cohort members were successfully traced. Deaths among white male hourly workers were 80 percent of expected, and non white hourly and white salaried workers had death rates 56 and 61 percent of expected, respectively. Mortality due to vascular lesions of the central nervous system and respiratory disease that was not malignant was much lower than expected. Mortality due to neoplasia showed a marked excess risk for brain tumors among all hourly workers. A slightly elevated risk was found for leukemia and very low risks for cancers of the buccal cavity and pharynx, stomach, rectum, and gential organs. Salaried workers had no deaths from brain tumors, with 1.5 expected. The standardized mortality ratio for brain tumors increased with increasing duration of employment. A total of 22 deaths from brain tumors occurred in hourly workers from 1941 to 1979, with 10.7 expected. The authors conclude that there may be an occupational cause for brain tumor deaths in petrochemical workers.