We took advantage of routine hemodynamic examinations to determine the relationship between splenic and intestinal circulation by infusing prostaglandin E1 into the superior mesenteric artery and observing the portal hemodynamic changes in patients with chronic liver disease. Relative blood flow rate in various vessels of the portal system were measured percutaneously using an ultrasonic duplex system, while portal venous pressure was measured directly using a transducer. The superior mesenteric venous blood flow increased significantly as did the portal venous blood flow and pressure, though the degree of change of portal venous blood flow was less than was expected from the change of portal venous blood flow in the superior mesenteric venous blood flow. Splenic venous blood flow decreased significantly. This decrease is perhaps due to a mechanism that acts to compensate for the increase induced in the superior mesenteric venous blood flow to maintain portal flow at approximately the same level. The measured changes suggest a relationship between splenic and intestinal blood flows that is regulated according to the hepatic circulatory condition. The regulatory mechanism should be considered when designing the treatment of portal hypertension.