This study evaluates the mortality experience of 9484 white men who worked at a petroleum refinery. We compared the numbers of deaths among these men during the period 1940 through 1984 with the numbers expected on the basis of the mortality rates of US white men. Overall, there were 2874 observed compared with 3568 expected deaths (standardized mortality ratio, 77). Mortality rates for most major cause of death categories and most cancers were also lower than expected. However, there was a statistically significant 50% excess of leukemia deaths (44 observed/29.6 expected). Lymphocytic leukemia was increased both among men hired before 1940 and among men hired in 1940 or later. In contrast, myelocytic leukemia was increased only among men hired in 1940 or later. The restriction of the myelocytic leukemia excess to men hired in 1940 or later may be related to process changes which occurred at the refinery after 1940 and which resulted in an increased percentage of benzene in certain refinery streams. The presence of an excess of lymphocytic leukemia, but not myelocytic leukemia, among men hired before 1940 suggests that some factor other than benzene was responsible for the former condition.