urethral carcinoma and hyperplasia in male and female b6c3f1 mice treated with 3344tetrachloroazobenzene tcab b6c3f1 mice chronically exposed to 3344tetrachloroazobenzene tcab a contaminant of dichloroanilinederived herbicides developed a number of neoplastic and nonneoplastic lesions including carcinoma of the urinary tract groups of fifty male and fifty female b6c3f1 mice were exposed by gavage to tcab at dose levels of 0 3 10 and 30 mgkg five days a week for two years control animals received corn oilacetone 991 vehicle decreased survival of male mice in the middose group and of male and female mice in the highdose groups was related mainly to the occurrence of urethral transitional cell urothelial carcinoma and resulting urinary obstruction increased urethral transitional cell carcinomas were seen in all treated male groups in a doserelated manner as well as in the females treated with 30 mgkg tcab administration of tcab was also associated with increased transitional cell hyperplasia of the urethra most nonneoplastic lesions of the urogenital tract were considered secondary to local invasion and urinary obstruction by the urethral transitional cell carcinomas the mechanism of tumor induction is uncertain but the high frequency of tumors in the proximal urethra of male mice suggests that the neoplasms result from the exposure of a susceptible population of urothelial cells to a carcinogenic metabolite of tcab