The entomological studies on malaria in Madagascar had especially concerned the behavior of vectors in relation to insecticides. The cessation of spraying within the homes and the absence of chloroquine allowed a re-emergence of malaria on the Plateau in the 1980's. This phenomenon pointed out the heterogeneity of the transmission on the island. It was necessary to define the entomological characteristics of the four principal facies of transmission in Madagascar. These studies provided the services of public health with the epidemiological basis to organize the measures of the battle and prevention of malaria. In the very populated countryside of the Plateau, the nature of the vectors, their density and their vectorial competence present large local variations. The entomological studies search to define the different human and environmental factors which modulate the transmission and constitute the risk factors of epidemy. This micro-epidemiological approach will facilitate the analysis and comparison of the clinical and biological results obtained in the different residences. The research on medical entomology will equally enable the proposal of plans for the fight against malaria adapted to the different situations.