In a retrospective cohort study, the observed mortality of employees of four United States carbon black producters was compared with that expected on the basis of population death rates of the states in which the plants were located. Of 190 deaths among carbon black workers, 29 were due to malignant neoplasms and 89 were due to heart disease. Observed deaths of workers did not exceed expectation in any of the diagnostic categories examined. The results of this study suggest that exposure to carbon black does not increase workers' risk of mortality from malignant neoplasms of heart disease above those of the populations from which they are drawn.