In seven anesthetized dogs the effects of intravenously administered prostaglandin E₁ on mesenteric arterial and portal venous blood flows and pancreatic capillary blood flow were measured with a transit-time ultrasonic volume flowmeter and a laser Doppler flowmeter. Basal blood flow of the superior mesenteric artery and of the portal vein were 5.7 ± 0.6 and 11.2 ± 1.0 ml/min/kg, respectively. Prostaglandin E₁ caused a dose-dependent increase in these blood flows. The maximal effect was observed at a dose of 10μg/kg, when the superior mesenteric arterial blood flow increased 117.9 ± 3.2% and the portal venous blood flow increased 99.4 ± 1.7%. Prostaglandin E₁ produced an initial rapid increase, followed by a decrease in pancreatic capillary blood flow. The results indicate that the flowmeters used in the present study are widely available for the study of splanchnic circulation and may have a possibility for clinical application.