The activities of artesunate-cotrimoxazole and artesunate-amodiaquine combinations against asexual-and sexual-stage parasites were evaluated in 182 Nigerian children with uncomplicated Plasmodium falciparum malaria. One hundred and twenty-one children received artesunate-cotrimoxazole and 61 received artesunate-amodiaquine and all were followed up for 28 days. Clinical recovery from illness occurred in all children. There was no significant difference in fever clearance time (P = 0.35). Both treatment groups achieved a parasite clearance time of less than 2 days (1.84 +/- 0.66 days and 1.31 +/- 0.48 days); gametocyte carriage rates were comparable in the two treatment groups prior to and following treatment; both treatments appeared to reduce gametocyte carriage. The pretreatment gametocyte sex ratio, which was female-biased, was maintained throughout the period of follow up in both treatment groups. Reduction of gametocyte carriage by these two treatment regimens may reduce transmissibility in P. falciparum malaria, and this reduction is presumed to be related to the accelerated clearance of the asexual forms of the parasite.