The effects of ketoconazole (KT) on the hepatic excretory function was investigated in the isolated perfused rat liver. KT, at the concentrations of 5 X 10(-5) M or 10(-4) M caused dose-dependent decreases of the biliary bile acid concentration and excretion rate, with no significant effect on bile flow rates. Neither dose altered perfusate flow through the liver. Furthermore, at the same two concentrations, KT impaired the sulfobromophthalein transport in a dose-dependent manner. In contrast, the drug did not alter 14C-sucrose bile to perfusate ratio and did not cause enzyme release from the liver into the perfusate. The study demonstrates that KT possesses an intrinsic toxicity in the isolated perfused rat liver and suggests caution in the use of this drug in hepatopathic patients.