Studies with human and rabbit effector cells demonstrated that ADC [antibody-dependent cytotoxicity] does not correlate with numbers of complement-receptor lymphocytes. The interaction between complement component 3 [C3] and the complement receptor alone was insufficient to trigger ADC, despite the capacity to bind to C3 receptor-bearing cells. In the presence of target cell-bound immunoglobulin G, binding through the complement receptor could be shown to enhance ADC.