Two hundred and thirteen Hondurans were treated for acute malaria with hydroxychloroquine or Plaquenil® (7-chloro-4-[4-(N-ethyl-N-β-hydroxyethylamino)-1-methylbutyl-amino] quinoline diphosphate). Twenty-five of them received a single oral dose of 0.75 gram and 125 received 1.25 grams. Twenty-six others with P. falciparum infections were given an intravenous dose of 0.36 gram in 500 cc. of normal saline, and 37 with P. falciparum infections were given 0.36 gram intramuscularly in 9.0 cc. of saline. Except with the lower oral dose, both the immediate and late results were quite good—comparing favorably with the other 4-aminoquinolines in common use. Toxic side effects were not noted on any of the regimens.