We tested the effect of various imidazole derivatives applied topically, on P-450-dependent enzyme activity of a reconstructed epidermis in conditions simulating clinical use. At nontoxic concentrations (determined by a cytotoxicity test based on the reduction of a tetrazolium salt, MTT, by mitochondrial deshydrogenase) econazole and clotrimazole had a biphasic effect on 7-ethoxycoumarin-O-deethylase (ECOD) activity in the epidermis, with induction at low concentrations and inhibition at high concentrations. Dermatological preparations (emulsions, gels) containing imidazole derivatives, which are nontoxic for the epidermis, decreased ECOD activity by about 40% 18 h after topical application. These results are in keeping with in vivo observations after topical application, and stress the value of the reconstructed epidermis for pharmacotoxicological and mechanistic studies of topical agents used in dermatology.