Plasmodium falciparum susceptibility to chloroquine and sulfadoxine/pyrimethamine was investigated in children living in an urban district of Ouagadougou, Burkina Faso, in August 1992. A modified WHO Standard Field in vivo test was used, with follow-up on days 2, 4, 7, and 14 after treatment with 25 mg chloroquine per kg body weight given over 3 days, or with standard doses of sulfadoxine/pyrimethamine in children from 2 to 8 years old with P. falciparum monospecific infection, asexual parasitaemia > 800/microliters of blood and negative Bergqvist and Lignin urine tests. Out of a total of 515 children screened, 152 were selected and randomized into treatment with chloroquine (86 children) or sulfadoxine/pyrimethamine (66 children). With the chloroquine regimen, parasitaemia did not clear by day 7 in 7 cases (8.1%), and there was recurrence of parasitaemia in 21 subjects (24.4%) on day 14, while all the children who had received sulfadoxine/pyrimethamine were fully sensitive on day 7 and day 14. It can be concluded that sulfadoxine/pyrimethamine is a good alternative for the treatment of falciparum malaria in areas of Burkina Faso with established chloroquine resistance.