The International Center for Medical Research (CIRMF) is located in an area highly endemic for malaria in southeastern Gabon, where humans and apes (gorillas and chimpanzees) are living in the same geographic area. The presence of the CIRMF primate center housing apes (59 chimpanzees and nine gorillas in 1994) within the city of Franceville provided an opportunity to investigate the capability of cross-transmission of malaria species from humans to apes. The main vector of human malaria, Anopheles gambiae, was found in the primate center and in a nearby populated area of Franceville. Despite high malaria transmission in humans of both Plasmodium falciparum and P. malariae (mean of 43% cumulative prevalence in schoolchildren), none of the apes were found infected with plasmodia during a six-month investigation. However, low antibody levels against sporozoite and blood stages of both P. falciparum and P. malariae were detected in a few chimpanzees and gorillas. These results demonstrate that only rarely would apes be bitten in the field by mosquitoes infected with human malaria parasites. In the case of infection proven by serology, we did not find any evidence that blood-stage malaria parasites were able to the gametocyte stage. The absence of any established malaria transmission cycle within the primate colony of CIRMF indicates that apes cannot be considered as animal reservoirs for human malaria parasites in this environment.