Abstract: When pyronaridine was given ig to 2 infected monkeys at a single dose of 6 mg (base)/kg, parasitemia was not cleared, but it was cleared in three of four monkeys treated at dosages of 6 mg/kg/d×3. With chloroquine at a single dose of 6 mg/kg, parasitemia of 2 monkeys turned negative, so did the parasitemia of 4 other monkeys treated at dosages of 6 mg/kg/d×3. Five of 6 monkeys treated with pyronaridine at 30 mg/kg recrudesced whereas only 1 of the 6 monkeys receiving the same dose of chloroquine recrudesced.