OBJECTIVE Portal circulation, in particular the contribution of the inferior mesenteric vein, can be evaluated in a relatively noninvasive way by per rectal portal scintigraphy (J Nucl Med 1988; 29:460-5). The clinical usefulness of the method was evaluated. METHODS A solution containing technitium-99m pertechnetate was instilled into the rectum, and serial scintigrams were taken while radioactivity curves for the liver and heart were recorded sequentially. By analyses of the curves, the per rectal portal shunt index (SI) was calculated. RESULTS The SI was higher for disorders that were more severe, increasing in the order of chronic persistent hepatitis, chronic aggressive hepatitis, and cirrhosis, and the SI was higher in cirrhotic patients than in patients with chronic hepatitis or in healthy subjects. The SI was significantly higher when a complication (varices, ascites, or encephalopathy) was present. Correlation between the SI and classic indicators for functional reserve was significant. The SI was significantly related to survival according to results of regression analysis by Cox's proportional hazards model. On the basis of the SI when patients were first examined, the patients with cirrhosis were divided into three groups of roughly equal size: group A, SI under 30%; group B, SI between 30 and 70%; and group C, SI over 70%. The survival rate was lower in group B than in A, lower in group C than in A, and lower in group C than in B. CONCLUSIONS This method is clinically useful, especially in establishing the prognosis.