Abstract: The tests of antibody-dependent cell-mediated cytotoxicity (ADCC)were performed to observe the kinetics of in vitro killing of Schistosoma japonicum schistosomula mediated by eosinophils, macrophages or neutrophils with infected mouse sera of different duration. The results showed that when complement was not involved, the killing rates of schistosomula mediated by eosinophils or macrophages began to increase significantly at 4 wk post-infection, reached a plateau in 5-7wk and 6-8wk respectively, and then declined to the levels of that at 4wk till llwk. In case of neutrophils, there was no significant cytotoxicity detected. When complement was involved, all the three effector cells could mediate cytotoxicity to schistosomula, with the killing rates higher than ihose without complement at the correspondent time intervals. These indicate that ADCC appears to be an important ingredient in the acquired resistance to S. japonicum, and demonstrate that eosinophil- and macrophage-mediated cytotoxicity to schistosomula is complement-independent, whereas neutrophil-mediated cytotoxicity to schistosomula is complement-dependent. This method may be of some value for chosing optimal time for vaccination and estimating the effectiveness of a candidate vaccine.