Elevated serum activities of alanine (ALT) and aspartate (AST) aminotransferases, suggestive of acute hepatocellular injury, occurred in 12 of 20 patients treated with lergotrile. Hepatic histology confirmed mild acute hepatocellular necrosis. Electron microscopy revealed hitherto undescribed ultrastructural changes in mitochondria of hepatocytes. When lergotrile was discontinued serum ALT and AST levels became normal in all patients. Elevated serum ALT and AST levels were much less frequent during bromocriptine therapy, occurring in 12 of 78 patients. Some of these abnormal values were only minimally elevated. Furthermore the elevated levels returned to normal without reducing the dose of bromocriptine. No patient in this study, receiving either lergotrile or bromocriptine, developed symptoms or clinical signs attributable to hepatic dysfunction.