DNA was extracted from the tumour tissue of 26 patients (18 smokers, 8 non-smokers) undergoing surgery for gastric cancer, and analyzed for the presence of DNA adducts by the 32P-post-labelling method. Adducts were detected in all samples tested, and adduct levels ranged from 2 adducts/108 nucleotides to 60 adducts/108 nucleotides. In male subjects, adduct levels were significantly greater in the DNA of smokers than in that of non-smokers. These results support epidemiological data suggesting that smoking is a risk factor for gastric cancer. © 1992 Wiley-Liss, Inc.