The incidence and nature of pruritus induced by chloroquine and halofantrine were studied in 82 patients with acute malaria and in 40 healthy subjects, using a visual analogue scale for quantitating pruritus. Results showed that the proportion of patients with acute malaria manifesting itch to halofantrine was significantly lower than the proportion manifesting itch to chloroquine. Furthermore, the intensity and duration of halofantrine-induced pruritus were significantly lower than those of chloroquine-induced pruritus. The few patients who itched to halofantrine all had a history of itching to chloroquine. The incidence and intensity of chloroquine-induced pruritus were significantly higher in patients with malaria than in healthy subjects. By contrast, there was no significant difference between malaria patients and healthy subjects as regards halofantrine-induced pruritus. These results suggest that itchers to halofantrine may constitute a small group within the population of itchers to chloroquine. Malaria infection appears to enhance chloroquine-induced pruritus but not halofantrine-induced pruritus and this may be of therapeutic importance.