The aim of our study was to investigate the suitability of Fao cells, derived from the Reuber H3 5 rat hepatoma as a tool for studying regulation of drug-metabolizing enzymes and drug metabolism. Fao cells express P450 2B, 2E, 3A and GST π and were used to study the effects of different inducers on these enzymes. Ethanol considerably increased the amounts of P450 2E and, to a lesser extent, P450 2B and GST π mRNA and protein. Dexamethasone decreased the amounts of P450 2B, 3A and GST π mRNAs, but had no appreciable effect per se upon the protein concentration of these enzymes. However, it antagonized the induction of P450 2E, 2B and GST π by ethanol, even at the protein level. RU 486 decreased P450 2B protein and P450 2E mRNA and protein levels without effecting P450 3A and GST π expression. RU 486 did not antagonize the dexamethasone effects, suggesting that at least some of these effects are not mediated by the glucocorticoid receptor. These data indicate that these cells constitute a suitable tool for studying the regulation of drug-metabolizing enzyme expression and drug metabolism.