Using a geographic information system (GIS),the microepidemiology of malaria was studied in an area of 8 square km in Matola ,a densely populated periurban area of Maputo southern Mozambique. Integrating data on the geographic location and characteristics of the houses in the study area, and malariometric data ,the risk of malaria in relation to proximity of the main mosquito breeding sits was described. Inhabitants of five cluster of hauses located at different distances from the maim mosquito breeding sites ,were enrolled in an open cohort and followed for 18 months ,from December 1993 to June 1995. Bimonthly cross- sectional surveys, were carried out to estimate the prevalence of malaria in the cohort. Body temperature and consumption of chloroquine were evaluated.