The pharmacokinetics of diazepam in normal rats and in rats pretreated with carbon tetrachloride to induce hepatic cirrhosis (cirrhotic rats) was studied after intravenous and oral administration of the drug (4 mg/kg). Animals pretreated with this hepatotoxic agent showed a significant prolongation in the half-life of diazepam in plasma that is due more to an increase in volume of distribution rather than to a decrease in clearance. This study confirmed that diazepam was highly extracted by the rat liver and was not affected by the hepatotoxic agent, although there probably was a saturation of the activity of the cytochrome P450 enzyme when the drug was administered orally. Diazepam binds to plasma proteins to a high degree in both normal and cirrhotic rats; however, in the latter, a significant increase in the fraction of unbound drug in plasma was observed. Pretreatment of rats with carbon tetrachloride did not produce any change either in the distribution of diazepam into erythrocytes or in the disposition of the metabolite desmethyldiazepam.