Plasmodium falciparum in vitro susceptibility to chloroquine, quinine, mefloquine and halofantrine was investigated in patients living in Bobo-Dioulasso (Burkina Faso, West Africa). Our study was carried out from July to November 1997 at the Malaria Chemoresistance Reference Centre, Centre MurazIOCCGE. Inclusion criteria were: presence of a single infection by R falciparum with a parasite count > or =4000 infected red cells/mm3. The susceptibility to drugs was measured after an incubation period of 48 hours at 37 degrees C, under 5% CO2. (3H) Hypoxanthine was added to the medium to monitor parasite growth. 134 isolates of P. falciparum were tested against chloroquine; 24.6% (33/134) were resistant. We have also documented 11.2% (15/133) of resistant isolates to halofantrine. All the tested isolates were susceptible to quinine (n=135) and mefloquine (n=136). A significant positive correlation was found between the following IC50 values: chloroquine-quinine, quinine-mefloquine and mefloquine-halofantrine. Our study shows no significant increase of the prevalence of chloroquine-resistant strains of P. falciparum in our study area; as well as the persistence of resistance to halofantrine with regard to previous publications in the subject.