In The Gambia, insecticide impregnation of bed nets, used alone or combined with Maloprim, reduced morbidity and mortality from malaria amongst children between one and 4 years of age. Taking expenditure of both time and money by public authorities and village volunteers into account, the costs and cost-effectiveness of each intervention were estimated. Bed net impregnation alone and the combined strategy cost US $5.65 and US $7.49 per child-year protected respectively (1990 figures). Insecticide (and drugs) accounted for more than 80% of the costs of each intervention strategy. They were both highly cost-effective. Estimated costs per death and per clinical episode of malaria averted were US $188 and US $28 for bed net impregnation and $257 and $19 for impregnation combined with chemoprophylaxis. Estimated costs per healthy year of life saved, discounted at 3%, were US $7.90 and US $10.84.