Population dynamics of the Anopheles gambiae complex of malaria vector mosquitoes were studied in four small hamlets in The Gambia. Bednets were used to reduce man/vector contact in two of the hamlets. High densities of An. gambiae, sensu lato, were present for only 3-8 weeks during the rainy season, depending on the position of the hamlet within the study area. The proportions of blood-fed mosquitoes caught indoors (83.0%) and existing from houses (11.6%) were lower in hamlets where bednets were used than in hamlets without (96.5% and 33.1% respectively). Fewer of the blood-fed mosquitoes had fed on man in houses where people slept under bednets (68.2%) than in those without (81.5%). However, the average number of infective bites received by children was still greater than one a year in hamlets where bednets were used. Consequently bednets are considered unlikely to be an effective malaria control measure so long as they are untreated with insecticide.