Serum complement levels in 200 patients with hepatic disorders or jaundice were determined in succesion by the 50% hemolysis method of Mayer. The following results were obtained. 1) In cases of acute hepatitis, serum complement levels (CH(50)) were high during 1～2 weeks after the onset and gradually returned to normal range in 4 weeks with the improvement of clinical symptoms. While, CH(50) levels in acute persistent hepatitis showed a slightly elevated value over 8 weeks after the onset of illness and fluctuated with exacerbations. 2) In cases of chronic hepatitis, CH(50) levels at the stage of remission remained in normal range and showed an indefinit fluctuation by relapsing. 3) CH(50) levels in liver cirrhosis were low and in some cases unable to be estimated and with exacerbations became lower gradually. 4) In cases of drug induced (toxic) hepatitis, CH(50) levels showed an markedly elevated value and remained high during a few weeks after jaundice had faded. 5) In cases of intrahepatic cholestasis with persistent jaundice, CH(50) levels were high and correlated well with serum bilirubin variation. 6) It wes observed that CH(50) levels showed a tendency to decrease in cases of chronic hepatitis and liver cirrhosis in which serum γ-globulin increased and RA factor or/and antihepatic antibody appeared.