A dynamic retrospective cohort study was performed to examine the mortality experience of 21,698 workers at Exxon's refineries and chemical plants in Baton Rouge, La.; Baytown, Tex.; and Bayway/Bayonne, N.J. Included were 15,437 regular employees who worked at least one month during the period Jan. 1, 1970, through Dec. 31, 1977, and 6,261 retirees who were alive as of Jan. 1, 1970. There were 137,702 person-years of observation. Mortality in this total study population was generally lower than that of the U.S. population. Study follow-up was complete for 98.7% of the study population. The standardized mortality ratio for the 3,198 deaths was 91, while that for deaths from all cancers (N = 666) was 94. Certain slightly elevated disease-specific mortality ratios, although not statistically significant, could be of biological importance and merit further review.