58 children aged 1 to 10 years who had pure Plasmodium falciparum infections acquired on the coast of Kenya were treated with chloroquine 25 mg/kg given over 3 d and erythromycin 10 mg/kg 4 times a day given for 7 d. After 4 weeks follow-up, 62% had recurrent infections and 11% failed to clear their parasitaemia (1 had an RIII pattern of resistance). Of 38 children treated with chloroquine 25 mg/kg alone, 55% had recurrences and 21% failed to clear (including 1 RIII). In vitro microtests classified 74% of isolates from initial infections and 91% of isolates from recurrent infections as resistant. Erythromycin does not improve chloroquine treatment in children with infections due to P. falciparum having low to moderate levels of chloroquine resistance.