Cytochrome P-450-dependent enzyme activities were detected in the Episkin model, a cultured reconstituted human epidermis. After topical administration of various mono-oxygenase substrates, 7-ethoxycoumarin (ECOD) and 7-ethoxyresorufin (EROD) de-ethylase activities were 0.92 and 0.39 pmoles/h/mug DNA, respectively, suggesting the presence of at least the cytochrome P-450 IA family. At a constant sate of penetration and metabolization, the metalbolization/penetration ratios were 0.025% for EC and 0.28% for ER. Both activities were highly inducible by topical application of 3-methylcholanthrene (8.5-fold for ECOID and 3.6-fold for EROD), Phenobarbital, a well-known inducer of hepatic cytochrome P-450, had no effect on epidermal ECOD activity, as previously reported in vivo. Topically applied testosterone showed a high degree of metabolization (17% of the quantity applied after 8 h). 5alpha-Dihydrotestosterone, 5alpha-androstenedione (5alpha-reductase activities), and 7alpha-OH, 2alpha-OH testosterone (steroid hydroxylase activities) were detected in control and benzanthracene-induced cultures. These data suggest that the Episkin model simulates some aspects of the metabolization of endogenous and xenobiotic compounds. This model should be suitable for testing interactions between nonhydrosoluble drugs or formulations and cutaneous metabolic capacities, and for assessing cutaneous xenobiotic absorption and biotransformation in vitro.