The resistance of P. falciparum to didderent anti-malarial drugs is present in many areas of the world where malaria is endemic. Chloroquine resistance has been reported in the Easten, Northern, Central and Western areas of Madagascar (1-10). Resistence has not yet been documented in the Southern areas. In view of this, a study was conducted in Southeast Madagascar to determine the in vitro susceptibility of P. falciparum isolates to chloroquine and mefloquine.