Calcium absorption, as measured by whole-body retention of isotopic (47)calcium, was investigated in 10 controls and 10 patients with primary biliary cirrhosis before and after medium-chain triglyceride therapy. Absorption of calcium was impaired in eight patients with primary biliary cirrhosis, three of whom had normal serum bilirubin. Mean absorption was significantly less in patients with primary biliary cirrhosis than in controls. Impaired calcium absorption correlated well with increased faecal fat excretion and less well with the intensity of jaundice. Osteoporosis was diagnosed radiologically in seven patients with primary biliary cirrhosis, and calcium absorption was restored to normal in seven out of eight patients after medium-chain triglyceride therapy. Decrease of steatorrhoea, weight gain, and relief of bone pain have been noted in most patients with primary biliary cirrhosis after therapy. It is concluded that bone disease occurs early in primary biliary cirrhosis, and early medium-chain triglyceride therapy in these patients is suggested.