Patients from Nigeria with uncomplicated Plasmodium falciparum malaria were treated with various antimalarials. Pruritis occurred in 8 of 56 patients treated with chloroquine at 25 mg/kg over 3 days, in 14 of 52 receiving the same dose of amodiaquine, and in 7 of 53 treated with 3 doses of 500 mg halofantrine 6 hours apart. Pruritis was not observed in 58 patients receiving 10 mg/kg quinine 3 times daily for 7 days, or in 82 that were treated with a single dose of 15 mg/kg of mefloquine. The onset of itching associated with halofantrine occurred between 7 and 30 h after the first dose, reached a peak in intensity 4-12 h later, and stopped 12-48 h after its onset. All patients who experienced pruritis when taking halofantrine had a personal or family history of itching associated with chloroquine, but not all patients with such histories reported pruritis when given halofantrine.