The in vivo metabolism of tritiated DMAB was examined in male Syrian golden hamsters, which are susceptible to both urinary bladder and intestinal carcinogenesis by this agent and in male F344 rats in which intestinal tumors represent the main lesions. Evidence was obtained for the presence of the N-hydroxy-N-glucuronide of DMAB as a major metabolite in hamster urine and bile and in rat bile but not urine. The routes of excretion of this metabolite, which may represent a transport form of the ultimate carcinogen, correlate well with the main tumor sites in the two species. Other metabolites partially identified were the sulfates and glucuronides of C-hydroxylated DMAB and C-hydroxylated-N-acetyl DMAB.