In 6 patients with cirrhosis of the liver and in 6 healthy controls the elimination half life of the serum leucine level (t 1/2 Leu) was determined after intravenous administration of 50 mg leucine per kg bodyweight. Examinations were repeated with simultaneous administration of 0,33 g glucose per kg bodyweight and during a continuous infusion of 500 microgram somatostatin over 60 minutes. The following results were obtained: 1. In cirrhotics and in healthy controls the t 1/2 Leu was shortened during the additional glucose administration compared with the t 1/2 Leu after leucine administration alone and was prolonged by inhibiting insulin secretion by somatostatin. 2. In spite of significantly higher serum insulin levels the t 1/2 Leu in patients with cirrhosis of the liver was significantly prolonged compared with healthy controls after leucine administration as well after leucine and glucose administration. Therefore we conclude, that in patients with cirrhosis of the liver in spite of elevated serum insulin levels leucine as well as glucose are metabolized slower. These results are indicating peripheral insulin resistance regarding the assimilation of glucose and leucine (at least in patients with portocaval shunts).