Human neutrophils were treated with IFN-gamma or lymphotoxin and their interaction with the asexual blood forms of Plasmodium falciparum was studied by a radiometric assay and microscopy. The results showed that human neutrophils inhibited the growth of P. falciparum and killed the parasite via a phagocytic mechanism. The cytokines significantly augmented the neutrophil-mediated killing of the parasite. When compared with the effects of TNF-alpha similar results were seen although IFN-gamma and TNF-alpha were effective at 10-fold less the concentration of lymphotoxin. The maximum neutrophil-mediated parasite killing was seen in the presence of immune serum and the cytokines. These findings suggest that T cells regulate the antimalarial activity of neutrophils.