Abstract: ADCC activity in normal and malarious mice was examined by 51Cr release assay using antibody-coated chicken erythrocytes as target cells and mouse spleen cells as effector cells. ADCC increased significantly during the early period of infection (1 to 6 days after infection), and decreased during the mid and late period (the ninth, twelfth and eighteenth day after infection) in acute non-lethal malarious mice. ADCC change was related with the quantity of plasmodia inoculated intraperitoneally in early period of infection. The sera from malarious mice with increased or decreased ADCC could induce or inhibit normal spleen cell-ADCC respectively, suggesting that factors which might influence ADCC activity, were present in serum in different periods of infection. Inhibition of ADCC accompanied generally by an increase of circulating immune complexes, suggesting that the immune complexes might block normal ADCC,