1,2,4-Trichloro[14C]benzene (TCB) was administered po (10 mg/kg) and iv (10 mg/kg) to rats and rhesus monkeys. Urine was collected at 24 hr and the major urinary metabolites were quantified and identified. By 24 hr, the monkey had excreted 22% of the iv dose and roughly 40% of the po dose in the urine. Less than 1% of the radioactivity was found in the monkey's feces. An isomeric pair of 3,4,6-trichloro-3,5-cyclohexadiene-1,2-diol glucuronides accounted for between 48 and 61% of the urinary metabolites. Glucuronides of 2,4,5- and 2,3,5-trichlorophenol (TCP) accounted for 14 to 37%, and unconjugated TCP's accounted for 1-37% of the monkey's urinary metabolites. For the rat, 84% of the po dose and 78% of the iv dose were collected in the urine by 24 hr; 11% and 7%, respectively, were the amounts collected in the feces. Two isomers, 2,4,5- and 2,3,5-, of N-acetyl-S-(trichlorophenyl)-L-cysteine accounted for 60-62% of the rat's urinary metabolites. Free 2,4,5- and 2,3,5-isomers of trichlorothiophenol amounted to 33% of the urinary metabolites in the po dosed rats and 28% in the iv dosed rats; free 2,4,5- and 2,3,5-TCP's amounted to 1% and 10%, respectively. These results show that there is a sharp division in the types of conjugates formed in the metabolism of 1,2,4-TCB by the rat and rhesus monkey.