Antibody-dependent cell-mediated cytotoxicity (ADCC) has been intensively investigated in various fields of immunology. Its major function, however, may prove to be related to infectious or parasitic agents. In the case of a metazoan parasite such as Schistosoma mansoni as a target, a large variety of in vitro killing mechanisms have been described as variations of the classical pattern of ADCC. After the original discovery by Clegg and Smithers of a cytotoxic IgG antibody in monkeys, and its further observation in man and various animal models, many in vitro instances of cell-antibody cooperation have been evidenced. In these the antibody can bind primarily to the killer cell via its Fc receptor or to the target via its antigen binding site. The latter results in an opsonic event in which the target cell is first coated with antibody and then attacked by the killer cell.