A case-referent study on lung cancer was conducted in Cracow, Poland. Men dying of lung cancer within a 6-year period (1980-1985) formed the case group. The reference series was selected from death registers and was frequency-matched with the cases by sex and age. Deaths due to other respiratory diseases were excluded. Information on the occupation, smoking habits, and residency of 901 cases and 875 referents was collected from their next-of-kin. The combined effect of smoking and industrial exposure, in particular employment in steel or iron foundries, was investigated by multivariate analyses and was very well fitted by a multiplicative model. Foundry employment, in particular in the younger age (less than 70 years) group, occupational exposure to known carcinogens in other industries for more than 20 years, and smoking were found to be risk factors.