Abstract: A 48 hour in vitro test was conducted to compare the susceptibility of chloro quine-sensitive strain and chloroquine-resistant strain of Plamodium falciparum to chloroquine, two enantiomers of chloroquine, desethyl-chloroquine and the new antimalarial drug pyronaridine. All the 5 compounds similarly inhibited the chloroquine sensitive-strain. However, pyronaridine was much more active than chloroquine and its enantiomers against the chloroquine-resistant strain, whereas desethylchloroquine was less active.