1-Naphthylamine was administered p.o. to beagles for .apprx. 9 yr at a daily dose of 15 mg/kg (5 days a week). At autopsy, no tumors other pathological changes were observed in the bladders of any of these animals. With the possible exception of the excessive accumulation of lipofuscin in the hepatocytes of these dogs, no test compound-related pathological changes in other tissues of the body were observed. Analysis of the urine revealed the presence of small amounts of N-oxidation products (1-nitrosonaphthalene plus N-hydroxy-1-naphthylamine), ranging from 2.85-125 .mu.g, following a dose of 1-naphthylamine. The theoretical significance of these findings is discussed.