In ten otherwise healthy patients undergoing cholecystectomy and cholangiography, morphine sulfate, in a dose of 2.5 mg/70 kg body weight, significantly elevated common bile duct pressure, as measured by water manometry, two and five minutes after intravenous injection. There was no added effect from an additional 7.5 mg/70 kg, measured two and five minutes after injection. Naloxone hydrochloride, in a dose of 1.0 mg/70 kg body weight, quickly reversed the increase in pressure caused by the morphine. Radiographic contrast material passed into the duodenum in every patient after administration of naloxone.