We conducted a prospective study from September 1997 to January 1998 in Libreville (Gabon). Fifty-three (53) children with uncomplicated P. falciparum malaria were included and divided into two groups. The first group (27 patients) was treated with amodiaquine and the second (26 patients) with chloroquine. The efficacy and tolerance of amodiaquine 30 mg/kg base over 3 days (10 mg/kg daily) and chloroquine 25 mg/kg base over 3 days (10 mg/kg day 0, 10 mg/kg day 1, 5 mg/kg day 3) were estimated at days 7 and 14. Clinical examination and parasitaemia were assessed on days 0, 1, 2, 3, 7, 14. Haematological and biochemical parameters were determined on days 0 and 7. Amodiaquine was shown to be more effective than chloroquine in clinical response and ridding patients of parasites: adequate clinical response was significantly higher with amodiaquine than chloroquine [100% (27/27) versus 45% (9/20), p < 0.0005]. Rates for early treatment failure (ETF) and late treatment failure (LTF) were respectively 35% and 12% with chloroquine. The parasitological success rate was significantly higher with amodiaquine than chloroquine on days 7 [93% (25/27) versus 62% (13/21), p < 0.008] and 14 [100% (13/13) versus 44% (4/9), p < 0.01]. The RI resistance type was 7% in the amodiaquine group. The rate of in vivo chloroquino-resistance was 53%, essentially of RII and RIII type. Overall, the two drugs were well tolerated.