Although both low socioeconomic status and cigarette smoking increase health problems and mortality, their possible combined or interactive influence is less clear. On one hand, the health of low status groups may be harmed least by unhealthy behavior such as smoking because, given the substantial health risks produced by limited resources, they have less to lose from damaging lifestyles. On the other hand, the health of low status groups may be harmed most by smoking because lifestyle choices exacerbate the health problems created by deprived material conditions. Alternatively, the harm of low status and smoking may accumulate additively rather than multiplicatively. We test these arguments with data from the 1990 U.S. National Health Interview Survey, and with measures of morbidity and mortality. For ascribed statuses such as gender, race, and ethnicity, and for the outcome measure of mortality, the results favor the additive argument, whereas for achieved status and morbidity, the results support the vulnerability hypothesis--that smoking inflicts greater harm among disadvantaged groups. (Contains 4 tables, 1 figure, and 9 notes.)