In the present study, male Göttingen minipigs received 15 mg/kg phenobarbital (PB) daily by the oral route for 6 days, followed by investigation of phase I and II liver enzymes (mRNA expression and enzyme activities), circulating thyroid hormone levels and differential gene expression in the liver. PB-treated minipigs had increased absolute (by 46%) and relative (by 42%) liver weights with mild, diffuse hepatocellular hypertrophy when compared to untreated control animals. PB-treated minipigs had reduced plasma concentrations of T3 (by 27% and 47%) and T4 (by 15% and 20%) at 24 hours and after 6 days administration, respectively as compared to predose values. PB-induced increases in hepatic CYP activities compared to control animals included: 5.0-fold increase in CYP1A2, 13.9-fold in CYP2B22, 2.4-fold in CYP3A29 and 1.6-fold in CYP4A24 activity, with corresponding increases in mRNA expression of these genes. A 1.6-fold increase in T4-UGT phase II activity was observed in PB-treated minipigs, which together with the liver weight increases lead to a treatment-related 4.9-fold increase in liver T4-glucuronidation capacity. In the PB-treated group CYP2A19, CYP2B22, CYP2C42, CYP3A39 and CYP3A46 were among the top 20 upregulated genes. These findings suggest that several of the early biochemical key events in the PB-induced rodent MOA are present in minipigs among biochemical and tissue-level changes observed. It is concluded that the minipig is a useful model for the study of effects on metabolism and the consequences of xenobiotics on the liver-thyroid axis.