The nature of the interaction between smoking of occupational exposure is controversaial. in part because of lack of agreement on the definition of interaction and in part becaue of the searcity of adequate epidemiologic data. Occupational investigators have assessed interaction primarily as a departure from an additive rather than from a multiplicative model of realtive risks (or rate ratios). To determine whether smoking modifies the effect of occupational lung carcinogens, the literature was reviewed for the only our established occupational lung carcinogens for which there are data on smjoking; radion daughters, asbestos, arsenic, and chloromethyl ethers. Wehre possible, departure was assessed from both an additive (syngergism) and a multiplicative model (effect modification). Only nine studies were considred to have sufficient ample size and to provide sufficient information on tobacco use and occupational exposure to evaluate interaction. The existing data were contradictory for three of the agents studied; as bestos, radon daughters, and arsenic. Inconclusive or contradictory fidnings may result from small sample size or lack of comparability of the level of occupational or tobacco exposure. It is noteworthy that, for these four agents, whenever smoking did modify the effect of occupatioanl exposure, the lung cancer rate ratio was greater for nonsmokers (compared to nonexposed smokers). However, with the exception of chloromethykl ethers, absolute lung cancer rates were higher for smokers than nonsmokers, regardless of occupational exposure.