A longitudinal entomologic study was carried out in the village of Ganse located in the Northeastern Ivory Coast from July 2000 to July 2001. The threefold purpose of the study was to index Plasmodium-carrying Anopheles species by capturing mosquitoes on human volunteers, collecting larvae in different dwelling types, and evaluating the involvement each species in the malaria transmission. A total of 4 species belonging to the Anopheles genus were collected in the village. Identification of circumsporozoite protein using the ELISA technique demonstrated that three species were plasmodium vectors. These species belonged to the An. gambiae complex (An. gambiae s.s. 100%), to the An. funestus group (An. funestus s.s. 95.6%) and to the An. nill group (An. nili s.s. 100%). The estimated mean sporozoite index was 5.9% for An. gambiae s.l., 4.3% for the An. funestus group and 2.6% for the An. nili group. The main larva breeding sites were standing water such as puddles for An. gambiae s.l., streams with tall plants for the An. funestus group and the Comoe River for An. nili group. Because peak breeding of these three species occurs at three successive times; i.e., in May, September and July respectively, transmission of P. falciparum is continuous throughout the year. The transmission rate is high since we recorded up to up to 410 infected bites per person per year. In addition to showing the presence of An. rivulorum-like, our findings in the area demonstrates the important role of An. nili s.s. in the transmission and the complexity of the vectorial system.