In some of the sera from patients with amoebiasis circulating immune complexes are present which are thought to interact with lymphoid cells, enabling them to elicit a burst of oxygen consumption in PMNs. The intensity of chemiluminescence is related to the presence of C3+ and Fc IgG+ cells in the lymphoid cell suspensions employed. The generation and release of highly reactive oxygen derivatives from PMNs impair T lymphocyte proliferative responses to the E. histolytica mitogen. The Authors suggest that one of the mechanisms by which circulating immune complexes present in the sera of patients with amoebiasis may interfere with T cell-mediated immune responses, is through their binding to the surface of the C3+, Fc IgG+ cells with subsequent stimulation of the PMN oxidative metabolism.