Epithelial cells from urinary bladders of pigs were isolated and cultured under serum-free conditions. For these cells it was previously shown that they developed morphologic polarity resembling the epithelium in vivo. Lactate dehydrogenase release was low, chromosome set and activities of marker enzymes (alkaline phosphatase, acid phosphatase, g-glutamyltranspeptidase) were stable over a period of 4 wk. In this study, metabolic competence was evaluated by measuring activities of phase I and phase II enzymes. Activity of prostaglandin H-synthase was expressed in freshly isolated cells as well as in cultured cells, as were activities of the conjugating enzymes glutathione transferase, UDP-glucuronyltransferase and N-acetyltransferase. Cytochrome P4501A1 activity in freshly isolated cells amounted to 10-15% of the respective activity in the porcine liver, this activity was not detectable in cultured cells. No activity was seen in cultured cells after induction with methylcholanthrene and benz[a]anthracene. This cell culture system was used to detect genotoxic effects of substances suspected to induce bladder cancer by measuring the induction of sister chromatid exchanges (SCE). The aromatic amines 4-aminobiphenyl and 2-aminofluorene induced a concentration dependent increase of SCEs at non-cytotoxic concentrations. These results imply that urinary bladder epithelial cells are capable to perform metabolic activation which is required to generate genotoxic effects of aromatic amines. Therefore, this new cell culture system, representing the urinary bladder epithelium, is an effective tool in in vitro toxicology to investigate adverse effects of compounds, regarded or suspected to induce toxic effects in the bladder.