Various factors to influence serum complement activity were studied in hepatic disorders. The results were as follows: 1) The definit correlation was observed between serum complement hemolytic activity (CH(50)) and immune adherence activity (CIA(50)). As to the complement components in sera with low level of CH(50), C 1, C 2 and C 4 activity were reduced and C 3 activity remained relatively normal. 2) CH(50) levels in patients with hypersplenism were subnormal and returned to normal range after splenectomy. 3) In 5 cases out of 72 patients with active chronic hepatitis, CH(50) levels in the normal range became suddenly unable to be measured by routine method and recovered normal after several weeks or months showing no change in the clinical features. The sera, at the stadium impossible to measure CH(50) levels, inactivated the complement activity of fresh human serum and guinea pig serum, and showed anticomplementary activity suggesting of Ag- Ab- C complex formation. 4) Most of anticomplementary activities in liver cirrhosis were suspected to be non-specific reaction due to abnormal protein metabolism. 5) There was a tendency of the low CH(50) level in cases of 6MP administration, while no influences on CH(50) level fluctuation in clinical course were found with glucocorticosteroids or azathioprine administration.