In order to test the hypothesis that endogenous opioids may mediate some of the circulatory derangements in cirrhosis, we studied the haemodynamic effects of naloxone, an opioid antagonist, in patients and in a rat model of biliary cirrhosis. In 9 patients with alcoholic cirrhosis and 5 control patients without significant liver disease, cardiac output, systemic vascular resistance, mean arterial pressure, heart rate, hepatic venous pressures and O2 content, hepatic and azygos blood flows and serum catecholamines were measured before and 30 min after naloxone 3.2 mg i.v. bolus. No significant changes were observed in either group of patients. Similarly in 16 conscious rats, 8 sham-operated and 8 with cirrhosis due to bile duct ligation, cardiac output, systemic vascular resistance, mean arterial pressure, heart rate, and splanchnic organ blood flows were measured by radioactive microspheres, before and 20 min after naloxone 1 mg/kg i.v. bolus. No significant changes were observed in either group. We failed to detect any evidence that endorphins are involved in tonic haemodynamic control in cirrhosis.