The present study characterized the antibody-dependent cellular cytoxicity (ADCC) of leukocyte effector cells (neutrophils, lymphocytes, and monocytes) from normal subjects and from chronic granulomatous disease (CGD) patients. CGD phagocytic cells (neutrophils and monocytes) had depressed ADCC activity against antibody-coated human erythrocyte (HRBC) targets in suspension cultures indicative of abnormal intracellular postphagocytic killing. However, when phagocytosis was prevented by using a monolayer of antibody-coated HRBC targets, CGD monocytes, neutrophils, and lymphocytes exhibited normal ADCC activity. Similarly, antibody-coated HRBC targets in suspension could be lysed normally by CGD effector cells when phagocytosis was inhibited by the addition of in vitro colchicine. Extracellular lysis of autologous antibody-coated lymphoid cell targets in suspension was mediated normally by CGD effector cells. Thus, standard ADCC against HRBC targets in suspension is predominantly indicative of postphagocytic killing and, as such, is dependent upon a normal post-phagocytic respiratory burst of oxidative metabolism which is deficient in CGD neutrophils and monocytes. Extracellular killing of sensitized targets does not appear to be dependent upon the generation of hydrogen peroxide (H2O2) ANd/or superoxide (02-) and is normal in CGD neutrophils and monocytes. Hence, by employing CGD leukocytes as investigative probes in ADCC, fundamental mechanisms of intracellular vs. extracellular expression of cytotoxicity have been delineated.