Previous studies have demonstrated that the organic cation 1-methyl-4-phenylpyridinium (MPP+) is avidly taken up by rat freshly isolated hepatocytes through at least two distinct transport mechanisms: the type I hepatic transporter of organic cations and P-glycoprotein. In this study, the effects of extrahepatic cholestasis induced by bile duct ligation for 4 days on the uptake of [3H]MPP+ by rat freshly isolated hepatocytes and liver slices were determined. Bile duct ligation produced no significant alterations in the characteristics of [3H]MPP+ uptake by freshly isolated hepatocytes. The strong correlation found between the effect of various drugs on [3H]MPP+ uptake by hepatocytes from control and treated rats (r = 0.958; P < 0.0001; n = 15) suggests that neither the type I hepatic transporter of organic cations nor P-glycoprotein were affected by bile duct ligation. On the contrary, uptake of [3H]MPP+ by liver slices was markedly changed after bile duct ligation: (1) there was a significant increase (approximately equal to 40%) in the amount of [3H]MPP+ taken up by liver slices from bile duct-ligated rats; (2) there was no correlation between the effect of various drugs on [3H]MPP+ uptake by liver slices from control and treated rats (r = 0.772; P= 0.072; n = 6). On the basis of (1) the lack of effect of bile duct ligation on [3H]MPP+ uptake by isolated hepatocytes; and (2) the profound morphological alterations of liver tissue observed 4 days after bile duct ligation (increase in volume density of bile ductules, ductular cells and infiltration of inflammatory cells), we suggest that non-parenchymal liver cells have an important participation in the hepatic uptake of [3H]MPP+ after bile duct ligation in the rat.