In a case-control study, 403 male patients with a diagnosis of "bladder tumor" and (as controls) 426 patients suffering from prostate disease were investigated. The results of this study indicate that past employment as a painter was associated with an excess risk of bladder tumor. The relative risk of bladder tumor estimated for painters was 2.76. The possible role of benzidine-based azodyes (or azodyes based on substituted benzidines) as a carcinogenic risk factor for painters is discussed.