Cyclosporine and hydrocortisone are the main immunosuppressants used in transplant surgery. The purpose of this study was to determine the effect of intravenous administration of cyclosporine and hydrocortisone on bile flow in dogs. Cyclosporine in doses of 0.5, 1.0 and 1.5 mg · kg−1 · hr−1 and hydrocortisone in doses of 1.25, 2.5 and 5 mg · kg−1 · hr−1 were administered along with 18 μmol/min intravenous sodium taurocholate to dogs with chronic biliary and gastric fistulas. Bile volume and bile chloride concentration and output were increased by cyclosporine in a dose-related manner, whereas bile salt concentration decreased and bile salt output was unchanged. Hydrocortisone produced small but significant increases in bile flow only at the highest dose of hydrocortisone administered. Subsequently, experiments were performed when sodium taurocholate was administered in progressively increasing doses (9, 18 and 36 μmol/min), with the dose changed every hour. Bile volume, [14C]erythritol clearance in bile and bile salt concentrations were measured with and without cyclosporine and hydrocortisone administration. Cyclosporine increased the bile salt-independent fraction of canalicular bile flow and ductular bile flow. Experiments evaluating the role of the cyclosporine carrier polyoxyethylated castor oil (Cremophor EL) demonstrated that this substance had no independent choleretic activity, whereas cyclosporine dissolved in ethanol and administered without Cremophor EL significantly increased bile flow. The results of this study indicate that cyclosporine stimulates chloride-rich choleresis independent of bile salt secretion.