The distribution of 3-hydroxykynurenine, a tryptophan metabolite that is suspected of being carcinogenic, was studied in mice. After s.c. administration of [3H]-3-hydroxykynurenine into male BALB/c X DBA/2 F1 mice, the distribution of 3H was investigated by whole-body autoradiography and radioactivity measurement. At 30 and 60 min after injection, 3H was distributed mainly in the kidneys, pancreas, liver, lung, and salivary glands. After 6 and 24 hr, 3H was retained only in the kidneys. After 30 min, about 70% of the radioactive compounds in the pancreas was unmetabolized 3-hydroxykynurenine, whereas most of the radioactivity in the kidneys, liver, lung, and submaxillary glands was derived from the other compounds. The data suggest that 3-hydroxykynurenine has an affinity for the pancreas.