The purpose of this study was to evaluate the impact of polymorphism of enzymes involved in metabolism of aromatic amines (N-acetyltransferase 2, NAT2) and polycyclic aromatic hydrocarbons (glutathione-S-transferase μ, GSTM1) in urothelial bladder cancer patients in an area of former coal, iron and steel industries.179 patients were phenotyped for NAT2 by HPLC according to their excretion of caffeine metabolites in urine. 92 patients were also genotyped from lymphocyte DNA for NAT2, 89 patients for GSTM1. All patients were interviewed for occupations ever performed for more than 6 months.64% of the 179 bladder cancer patients were slow acetylators. In 70% of a subgroup of 89 patients GSTM1 was lacking. Contrary to the normal distribution of slow acetylators which was observed in underground coal miners (18 of 32), all 5 coke oven workers were slow acetylators. GSTM1 was lacking in 16 of 19 underground miners and in all 4 genotyped coke oven workers. There was a normal distribution of NAT2 and GSTM1 in businessmen and administratives. The results are consistent with the view that slow acetylator status and the lacking of GSTM1 are individual risk factors for bladder cancer in persons occupationally exposed to aromatic amines and PAHs to a high extent.