Twenty-nine dogs anesthetized with Na-pentobarbital were laparatomized and liver blood flow was measured by 133Xe clearance method. Fifteen dogs of the experimental group were subjected to rapid i.v. glucose tolerance test whereas 14 animals of the control group were treated identically except for infusion of glucose. It was found that the arterial and the portal venous blood glucose rose significantly during the glucose tolerance test. Liver blood flow in the experimental group was 123.8 ml/100 g L/min after operative procedures. It reached 171.9 ml/100 g L/min at 10 min after infusion of glucose (P < 0.01). At 20, 30, and 40 min of the test it was 145.4 (P < 0.05), 143.4 (P < 0.01), 135.1 (P < 0.05) mg/100 g L/min, respectively. Liver blood flow did not change significantly during the observation period in the control series. It is concluded that glucose loading may produce some metabolic effects secondary to rising liver blood flow in addition to changes induced by its rising concentration.