Many animal experiments have been studied on the choleretic effects of secretin. We intended to estimate secretin choleresis in human (15 patients) who had received PTCD or T-tube insertion into the common bile duct. Based upon these data of secretin and choleresis, secretin was administered to 11 patients with prolonged jaundice due to intrahepatic cholestasis in order to evaluate this as a new therapy for intrahepatic jaundice. As controls, eleven patients with intrahepatic cholestasis treated with steroid hormones and/or phenobarbital were used. In all cases with biliary drainage, secretin produced a remarkable choleretic effect with a high concentration of bicarbonate. In 9 out of 11 patients with intrahepatic cholestasis who were treated with secretin, levels of serum bilirubin decreased linearly and other liver function tests returned to the normal range. The mean values of T1/2 (number of days required for reduction by half) of serum bilirubin in 9 effective cases to secretin was 10.8 days. On the other hand, that in 11 effective cases treated with steroid hormones and/or phenobarbital was 23.2 days. These results suggest that secretin therapy may be an effective treatment for intrahepatic cholestasis.