The in vitro activities of pyronaridine, alone and in combination with established antimalarial drugs, were assessed by isotopic microtest. Pyronaridine was highly active against all Cameroonian isolates. A positive correlation was observed between the response to pyronaridine and that to chloroquine. Drug combination studies showed synergy between pyronaridine and primaquine, additive effects with 4-aminoquinolines, and weak antagonism with dihydroartemisinin, antifolates, or amino alcohols.