1. The objective of this study was to determine the basal and inducible activities of several cytochrome P450 (CYP) isozymes and monitor the acinar and hepatocyte morphology in precision cut, cultured rat and mouse liver slices. 2. The slices were cultured up to 96 h in Chee's essential medium supplemented with insulin, transferrin, selenium, DMSO, dexamethasone and epidermal growth factor. A dynamic roller system was used to incubate the slices at 37 degrees C in an atmosphere of 95% O2:5% CO2. 3. Histopathology of the liver slices revealed maintenance of normal hepatic lobular architecture with time in culture. 4. CYP isozyme activities were measured at various times of culture. In rat liver slices, at 72 h, CYP1A1/1A2 activity was induced 4-fold by beta NF and 37-fold by dioxin (TCDD) whereas in mouse liver slices, 1A1/1A2 activity was not inducible by beta NF but was induced 19-fold by TCDD. At 72 h, CYP2A5 (coumarin-7-hydroxylase) activity was not detected in rat liver slices but in mouse liver slices, 2A5 was induced 2-fold by beta NF, 11-fold by phenobarbital (PB) and 3-fold by TCDD. 5. Hydroxylation of testosterone at specific positions was used as an indication of the activities of various P450 isoforms. Testosterone was added to the cultures at 0 and 72 h and the metabolites were measured at 24 and 96 h respectively by hplc analysis. Depending upon the species, the treatment and the time in culture, CYP1A, 2A, 3A, 2B and 2C activities were detectable. 3A activity was highly induced by PB in both rat and mouse liver slices. These results demonstrate that this culture system can be used to assess and compare xenobiotic metabolism in liver slices from rodent species.