Excessive hepatic copper accumulation occurs in long-lasting cholestatic liver disorders especially in primary biliary cirrhosis. As in Wilson's disease, penicillamine has recently been introduced for the treatment of primary biliary cirrhosis. In Wilson's disease there is decreased biliary excretion of copper. The present study shows that as compared with controls the biliary excretion of copper is not decreased in primary biliary cirrhosis; instead it may be increased in some patients. However, when compared with high hepatic copper concentration biliary copper excretion was low. In contrast with copper, biliary secretion of bile acids was decreased in eight of the 17 patients. Treatment with oral penicillamine (600 mg/day) for one year resulted in a significant decrease of hepatic copper concentration, but had no consistent effect on the biliary excretion of copper or on the amount of histologically stainable orcein-positive copper-binding protein. The results suggest that excessive hepatic copper accumulation in primary biliary cirrhosis may not be primarily caused by a decreased biliary excretion, or that a new equilibrium is achieved in advanced primary biliary cirrhosis. D-penicillamine appears to improve significantly the biliary excretion of bile acids.