We evaluated the efficiency of the simplified version of the isotopic microtest (simplified test) and compared it to that of the complete version (standard test), for determining the susceptibility of local strains of Plasmodium falciparum to chloroquine, quinine, mefloquine and halofantrine. The study was carried out from July to November 1996, at the MURAZ Center, Bobo-Dioulasso, Burkina Faso. The inclusion criteria were: single infection with P. falciparum, with a parasite count of at least 4,000 infected red blood cells per mm3. Susceptibility to each drug was determined after incubation for 48 hours at 37