A luminol-dependent chemiluminescence (CL) method was used to measure the oxidative burst of phagocytes triggered by antimalarial antibodies and Plasmodium falciparum merozoites. A specific antibody-dependent increase in chemiluminescence response was obtained using both polymorphonuclear leukocytes and monocytes as effector cells. Using various sera from malaria infected subjects it was observed that antibodies involved in the increased chemiluminescence responses were encountered at higher levels in sera from protected subjects than in those susceptible to clinical manifestations. In the conditions used the assay shows substantial intertest variation but appears of interest to assess the protective status of groups of exposed individuals.