Previous studies of the relationship between arsenic levels and respiratory cancer among copper smelter workers have not directly accounted for possible effects of SO2 exposure and cigarette smoking. This is a report on the 1949-1980 mortality experience of 6,078 white male workers who worked at least 3 years between 1 January 1946 and 31 December 1976 at one or more of eight US copper smelters. The completeness of the cohort was verified statistically, and worker exposures to arsenic, SO2, dust, nickel, cadmium, and lead were estimated from retrospective industrial hygiene surveys reported elsewhere. By using internal controls, a dose-response relationship for lung cancer was observed with exposure to arsenic and SO2. When cigarette smoking data were included with arsenic and SO2 exposure data in a nested case-control analysis, only smoking and arsenic were statistically significant factors. The arsenic-lung cancer relationship was confined to a single smelter associated with high content feed. In the remaining smelters mortality for all causes of death and for all cancer was not high based on comparisons with national, state, and local rates.