A group of 300 young European adults visiting Gabon for relatively short periods was surveyed monthly for malaria from a parasitological, clinical, immunological, hematological point of view. The regular increase of fevers due to malaria from 1984 to 1988 and the multiplication of cases of amino-4-quinoline resistance in the plasmodial parasites call for new prophylactic considerations for this group residing in this heavily malaria infested area.