Nine patients with unresectable primary and secondary malignancy of the liver underwent ligation of the hepatic artery (HAL) distal to the gastroduodenal artery as a therapeutic measure. Another patient had a similar operation for hepatic artery aneurysm. Their postoperative liver function tests are studied in detail, and the patterns of change are compared with three other patients who had extensive resection of tissues but without HAL. It appears that liver function tests rarely became abnormal after major operations, whereas HAL produced an immediate rise of lactic dehydrogenase and transaminase (up to 5--60 times normal value), and creatine phosphokinase (4--15 times normal). All elevated enzymes returned to preoperative levels within a week. Alkaline phosphatase and bilirubin rose mildly after HAL and returned to preoperative range in about one week. However, if the patient had repeated surgical stress, anoxic insult, or maximal loss of the hepatic parenchyma, serum enzymes rose only slightly after HAL.