Acetylation is one of the major routes in metabolism and detoxification of a large number of drugs, chemicals and carcinogens. Slow acetylators are said to be more susceptible to developing bladder cancer and because of investigations about tumor risk based on phenotyping procedures, it was our aim to study the distribution of allelic constellations of the N-acetyltransferase (NAT2) by genotyping patients with bladder cancer. We analysed NAT2 gene of blood and tumor DNA from 60 patients with primary bladder cancer and DNA of blood samples from 154 healthy individuals. Using ASO-PCR/RFLP techniques we identified 70% of patients with bladder cancer (n = 42) to be slow acetylators while genotyping of controls resulted in 61% with slow acetylators (n = 94). In addition, dividing bladder cancer patients in males and females the genotype NAT2*5B/NAT2*6A occured with much higher frequencies in males (OR = 4, 95%); CI = 1.8-8.9). Furthermore, investigating bladder cancer tissues we could detect loss of heterozygosity (LOH) in slow and rapid acetylator genotypes. In eleven out of 60 tumor samples (18.3%) we observed allelic loss at the NAT2 locus while in control DNA of blood from the same patients both alleles were still detectable.