N-acetyltransferase 1 (NAT1) modifies bladder cancer risk in European populations exposed to aromatic amines in cigarette smoke. The present study was performed to investigate a possible association between NAT1*10 and NAT1*14A genotypes and bladder cancer risk in benzidine-exposed Chinese workers. Based on the cytological gradings of exfoliated urothelial cells according to Papanicolaou, an exposed research cohort was stratified into subgroups. An allele-specific PCR-based procedure was used to detect the polymorphism in the polyadenylation signal at the locus NAT1 T(1088)A. A nested PCR-RFLP procedure was conducted to differentiate NAT1*14A (T(1088)A, C(1095)A, and G(560)A) from NAT1*10 (T(1088)A, C(1095)A). No significantly different frequencies of homozygous and heterozygous NAT1*10 alleles were found among the subgroups with (i) gradings according to Papanicolaou < or = II (18.3 and 40.2%, respectively), (ii) higher gradings according to Papanicolaou (> II; 28.0 and 34.1%, respectively), and (iii) with bladder cancer (26.3 and 34.2%, respectively). The present data show that NAT1*10 neither displayed an association with an elevated grading of urothelial cells nor a clear impact on the risk for bladder cancer in benzidine-exposed Chinese workers. Discrepancies with the findings in European populations could point to ethnic differences in the disposition of aromatic amines.