With recent advances in the field of complement research, much of the newer knowledge about the technique of assay has come from application of modern tools of molecular biology to the study of immune mechanism in various chronic diseases. In view of this, the author has carried out the studies on hemolytic complement activities and components of complement in chronic liver diseases. Sera from the total of 186 cases consisted of 105 cases of patients with chronic hepatitis, 31 cases of liver cirrhosis, and 50 normal controls served as the material for observations by micro titer method. The mean number with standerd deviation (m±S.D.) of 50% units hemolytic complement activity (CH 50) in normal controls were showed 67.20±15.40u. In the cases of chronic liver diseases, the number in chronic hepatitis were showed 44.75±27.40u. and in liver cirrhosis 45.55±31.28u. On the between of active form and inactive form in chronic hepatitis, CH 50 in the former were showed lower levels than in the latter. For the measurements of components, reactivity of each of the nine components (namely C1, C4, C2, C3, C5, C6, C7, C8 and C9) of complement were observed. The kind of component with lowest level in chronic hepatitis was observed as C4 in 89% out of all cases, and in liver cirrhosis as C3 in all. Furthermore, on the complement inactivator, C1-inactivator (C1-INA) was detected in 2 cases out of 36 cases of chronic hepatitis with low CH 50. Finally, C4-inactvating factor (C4-INAF) was appeared in the cases of 92% of chronic hepatitis with low CH 50, and in 50% of liver cirrhosis with low CH 50.