The pattern of chlorpromazine metabolites in human urine was studied by paper chromatography. Four highly water-soluble metabolites were isolated in 2 fractions by ion exchange. Incubation of these fractions with B-glucuronidase and subsequent paper chromatography showed the release of glucuronic acid and phenothiazine-like compounds with Rf values markedly different from those of the unhydrolyzed metabolites. The released phenothiazine-like compounds were extractable, in part, by ether from both an acidic and a basic medium. These results indicated that these 4 metabolites in urine were conjugated products of glucuronic acid and phenolic metabolites resulting from hydroxylation of the phenothiazine nucleus. Hydroxylation thus constitutes an important aspect of chlorpromazine metabolism.