Among 158 adults hospitalized at the University Hospital of Libreville who did not receive any treatment against malaria before blood screening, 20 were carriers of malaria parasites. Plasmodium falciparum was seen in 19 cases with a parasitic density lower than 1,000 trophozoits/mm3 of blood in 18 cases. The most important prevalence was observed into the group of older people. In most cases symptoms related to malaria did not occur during the hospitalization. We conclude that, in such patients, a parasitic density lower than 1,000 trophozoits/mm3 is not sufficient to assess the diagnosis of malaria and does not deserve systematic treatment.