The study by an isotopic semi-microtest of the sensitivity of 44 P. falciparum strains isolated from Congolese children living in Pointe-Noire demonstrated a high prevalence of chloroquine resistance and partial cross resistance to monodesethylamodiaquine. The sensitivity to quinine was high except for 3 isolates. The assay of amino-4-quinolines by H. P. L. C. on 37 subjects revealed the extent of self-treatment and drug-pressure in this population. A 3-day treatment with 25 mg/kg of chloroquine or amodiaquine in 24 subjects resulted in the disappearance of clinical symptoms in all patients and a parasitological cure on day 7 in 75%. The partial maintenance of efficacy of amino-4-quinolines in this chloroquine-resistant region implies that chloroquine and amodiaquine can be used as first choice drugs for uncomplicated acute malaria, but on condition that the levels of resistance and transmission are monitored.