Eosinophils and neutrophils are shown to be cytotoxic against two syngeneic mouse cell lines cells when these are coated with T. cruzi antigen and anti-T. cruzi antibody. Activity is detected within 5 h of incubation. Highest levels of cytotoxicity are obtained at antibody dilutions of 1:100 and 1:1000, while antiserum at 1:10 is shown to be inhibitory. Eosinophils show significant activity at an effector to target ratio of 5:1. No cytotoxicity occurs in the absence of either antigen, antibody or effector cells. This phenomenon may be a model for the tissue destruction in acute T. cruzi infection, where the lysis of trypanosomes may lead to antigen coating of host cells, followed by antibody-dependent granulocyte-mediated cytotoxicity of the host cells.