Abstract: The level of the serum C4, C3 and CIC was determined in 30 cases of late schistosomiasis. It was found that: (1) the level of C4 was lower in the patients than that innormal individuals, suggesting that activation of the classical pathway of complementdid occur in late schistosomiasis; (2) the level of CIC was elevated in the patienis,being negatively correlated with C4. C4 other than C3 is recommended for studying' the activation of classical pathway of complement in late schistosomiasis.