Metabolisms of the potent pancreatic carcinogens N-nitroso-bis(2-oxopropyl)amine (BOP) and N-nitroso-bis(2-hydroxypropyl) amine (BHP) were studied in male Syrian hamsters. BHP and a new metabolite, N-nitroso-(2-hydroxypropyl)(2-oxopropyl)amine (HPOP), were detected in the urine of hamsters administered BOP and BHP. The rates of HPOP formation from BOP and BHP were determined by the measurement of blood and urine levels at various times after each compound was administered: HPOP was formed readily from BOP, but slowly from BHP. This may explain the different organotropic spectra and carcinogenic potencies of BOP and BHP.