Incidence of P. falciparum malaria in french non-immune soldiers serving in Gabon for four months has increased from 21% in 1987 to 37% in 1988. Since 1989, in a first step, the personal protection measures were reinforced. Thereafter, the usual chemoprophylaxis (chloroquine 100 mg daily) was replaced by a daily association of chloroquine 100 mg and proguanil 200 mg. A 85% decrease of malaria incidence was observed in 431 soldiers. The effects of the personal protection strengthening and of the new chemoprophylaxis can be evaluated to be respectively responsible for 50% and 71% decrease. Among the secondary effects, gastric pain was the most frequent, but it was never a cause of chemoprophylaxis stopping. The mouth ulcer frequency was far lower than that elsewhere reported. No significant biological abnormalities could be related to the chloroquine-proguanil association.