A polymorphism at codon 105 (Ile/Val) in the GSTP1 gene has been associated with a higher risk for different cancer types. To assess the role of GSTP1 polymorphisms in the development of benzidine-related bladder cancer, GSTP1 AA, AG and GG genotypes were determined in occupationally benzidine-exposed Chinese workers without known disease and benzidine-exposed bladder cancer patients from the same cohort of the Shanghai area. An increased but not significant frequency of GSTP1 AG or GG carriers was observed in the occupationally exposed bladder cancer patient group [odds ratio (OR)=1.95, 95% confidence interval (CI) 0.70-5.46]. The odds ratios for the most important non-genetically determined risk factors for bladder cancer in male individuals were as follows: age (increase per year): OR 1.05, 95% CI 0.99-1.11; ever smoker: OR 1.31, 95% CI 0.47-3.69; duration of exposure (increase per year): OR 1.19, 95% CI 1.10-1.29; and high exposure: OR 4.50, 95% CI 0.70-5.46. Significant differences were found between all benzidine-exposed workers without known disease with modified exfoliated urothelial cells (grade II and higher) and all workers without known disease with at most minor changes (less than grade II) according to Papanicolaou (OR 1.90, 95% CI 1.13-3.20). These findings show for the first time an association between the GSTP1 AG or GG genotype and higher cytological gradings of exfoliated urothelial cells from formerly benzidine-exposed workers.