Chlorpromazine (CPZ) metabolites were studied for their phototoxic potency with the mouse tail technique. The demethylated metabolites were more phototoxic potency with the mouse tail technique. The demethylated metabolites were more phototoxic than CPZ, while CPZ-sulfoxide, 7-hydroxy-CPZ, and 2-chlorphenothiazine were less phototoxic. The phototoxicity of CPZ and desmethyl-CPZ preexposed to UVA was lost, while that of CPZ-sulfoxide was retained. By thin-layer chromatography, CPZ-sulfoxide and promazine were identified as photoproducts of CPZ; the sulfoxide was fairly stable to radiation.