A longitudinal study was conducted in the Yaounde area of Cameroon that involved 211 individuals in June 1990, and 70 individuals for the follow-up study in December 1990. Sera from these subjects were tested against the recombinant 96-thermoresistant antigen of Plasmodium falciparum and the kinetics of antibody production to this protein show that titers tend to increase with age and are also related to antigen exposure. The increase in antibody titers with age correlates positively with the ability of the individual to prevent development of a high parasitemia. Adults who maintained stable high titers generally did not experience clinical attacks during the study period. The data suggest that antibodies against the 96-kD antigen participate in conferring some immunity to falciparum malaria.