Crude merozoite antigens from Plasmodium falciparum were used to evaluate the proliferative response of peripheral mononuclear cells (PBMCs) from 114 inhabitants of the village of Dielmo (Senegal, West Africa) exposed continuously to malaria transmission. The high or low responses to merozoite antigens obtained in lymphocyte stimulation assays were correlated with the presence or absence of parasites, IFN-gamma production and HLA phenotype. The high responders produced high levels of IFN-gamma, in contrast to the low responders, most of whom did not secrete IFN-gamma (23/27). Among others, the two HLA phenotypes HLA-B51 and HLA-DR1 were significantly associated with a high response (P < 0.05).