Cyclosporine A is reported to cause cholestasis, but the evidence is confounded by anesthesia and surgery used in acute experiments. To better investigate the effect of cyclosporine on the liver, bile output was directly measured in three cholecystectomized dogs by cannulating the common duct through a chronic duodenal fistula. Control studies were done 1 month after surgery. Cyclosporine in oral doses of 5, 15, and 50 mg.kg-1.d-1 was then given for consecutive 1-week periods. Twice during each study period, bile output was measured for 5 h in fasted, awake animals: 3 h to establish basal conditions, followed by 2 h of taurocholate infusions at 1 and then 2 mumols.kg-1.min-1. Under basal conditions, bile flow rose with each dose of cyclosporine, increasing 63, 127, and 179% above control with cyclosporine 5, 15, and 50 mg.kg-1,d-1, respectively. Bile flow increased similarly during taurocholic acid stimulation. Cyclosporine had no effect on bile salt or bilirubin secretion. In this chronic dog model isolated from other causes of cholestasis, cyclosporine did not induce cholestasis but rather caused a dose-related choleresis without any change in bile salt secretion.