Portal circulation can be evaluated in a relatively noninvasive way by per-rectal portal scintigraphy. We used this method to evaluate portal hemodynamics in patients with chronic liver diseases and underlying hepatic viral infection; the patients did not need surgery or sclerotherapy, or refused it, so changes in the natural course were identified. A solution of Tc-99m pertechnetate was instilled into the rectum, and serial scintigrams were taken while radioactivity curves for the liver and heart were produced. The per-rectal portal shunt index was calculated from the curves. In a longitudinal study, 70 patients (9 with mild chronic hepatitis, 10 with moderate chronic hepatitis, 7 with severe chronic hepatitis, 22 with cirrhosis but without varices, and 22 with both cirrhosis and varices) were examined at least twice at intervals of 12-102 months (mean, 39 months). The shunt index was higher for more severe disorders, increasing in the order of mild chronic hepatitis, moderate chronic hepatitis, severe chronic hepatitis, cirrhosis without varices, and cirrhosis with varices. The mean annual changes in the mean shunt index were 1.0% in mild chronic hepatitis, 4.4% in moderate chronic hepatitis, 6.1% in severe chronic hepatitis, 10.7% in cirrhosis without varices, and 6.2% in cirrhosis and varices. Cirrhotic patients were arbitrarily divided into two groups of roughly equal size on the basis of the shunt index at the first examination. In those with a shunt index of 30% or more, the mean annual change was 4.7%. The patients with a shunt index of less than 30% had a mean annual change of 11.8%. Changes in the portal hemodynamics were not steady. The shunt index rose gradually as disease advanced from mild to moderate and to severe chronic hepatitis and cirrhosis of the liver, after which the index rose rapidly when varices developed, slowing later.