The occurrence of pain and changes in serum concentrations of liver enzymes and amylase were investigated after challenge with intramuscular morphine (0-12 mg/kg) and neostigmine (0-012 mg/kg) in 25 control subjects and 80 patients with undefined biliary type pain, both with and without prior cholecystectomy. Peak enzyme concentrations were reached at four hours after the injection of morphine-neostigmine. When compared with controls, patients who had pain after cholecystectomy and a dilated bile duct and/or spontaneous changes in liver enzymes, had a higher frequency of drug induced pain and a higher frequency of rise (>2×N) in serum concentrations of aspartate aminotransferase (AST) and amylase; postcholecystectomy patients with pain but without bile duct dilatation, and patients with pain without prior cholecystectomy, had a higher frequency of drug induced pain but did not have a higher frequency of enzyme rise. Increases in liver enzymes after morphine-neostigmine were abolished by endoscopic sphincterotomy. Thirty three patients with a dilated bile duct and/or spontaneous changes in liver enzymes were also studied by endoscopic manometry of the sphincter of Oddi: similar frequencies of enzyme changes were observed in patients with normal manometry as in those with various manometric disorders. Increases in serum concentrations of liver enzymes after morphine-neostigmine may be explained by high biliary pressures resulting from an exaggerated motor response in the sphincter of Oddi.