The interactions of amantadine with classical antimalarial drugs were evaluated against a chloroquine-resistant and a chloroquine-sensitive strain of Plasmodium falciparum in vitro. Amantadine potentiated the effect of chloroquine and quinine in both strains; it also potentiated the effect of mefloquine, halofantrine and primaquine in the chloroquine-resistant strain but had no effect in the chloroquine-sensitive strain. Amantadine had no effect on the response to pyrimethamine of either strain. Amantadine does not interfere with the activity of these compounds and may possibly enhance it.