Pharmacokinetic alterations in drug disposition have been demonstrated for a variety of hepatic disease states, but there is little information concerning the effects of elevated hepatic venous pressure on hepatic drug metabolism. A rat model of hepatic congestion which was characterized by significantly elevated hepatic venous pressure, marked prolongation of prothrombin time, reduced total hepatic blood flow and histological changes of marked pericentral fibrosis and central vein dilation was used to study the effects of liver congestion on hepatic microsomal biotransformation and in vivo disposition of morphine and pentobarbital. No significant differences in levels of microsomal cytochrome P-450 or NADPH-dependent cytochrome c reductase were seen between the two groups. Total hepatic microsomal capacity for glucuronidation of morphine and hydroxylation of pentobarbital was not altered by elevated hepatic vein pressure and no change in in vivo systemic clearance was seen for either drug in response to hepatic venous congestion. These animal data demonstrate that hepatic congestion produces minimal alterations in hepatic metabolism of morphine and pentobarbital and may not have the severe detrimental effects on drug biotransformation and disposition which would be predicted.