Indications were obtained that Australia antigen-antibody complexes are more frequent in patients with cirrhosis than in other Australia antigen-positive individuals. The evidences were: (1) Among sera with high titres of Australia antigen, anticomplementary activity was detected at lower dilutions in 53% of the cases of cirrhosis, as compared to 14 and 7% in hepatitis patients and carriers, respectively. (2) Among anticomplementary sera which did not show Australia antigen at higher dilutions, the antigen was unmasked after heating at 85 °C in 4 of 7 cases of cirrhosis and in 2 of 11 other patients. On the other hand, a new type of antibody was demonstrated in three patients who had experienced a progressive decrease of Australia antigen titre; the antibodies were detected after the disappearance of the antigen, but they reacted only with some antigenic component of Australia-positive sera which was unmasked after treatment with Tween 80.