The average biomass in the breeding places has been calculated on the basis of the near constant ratio of the young forms growing and the average number of each stage. The study of the annual cicle of the average biomass of five Anopheles populations has confirmed previous observation that these mosquitoes, in nature, have very slow development. in this study it has been evident also that the larvae density, as it classicaly has been calculated, by dividing the total of colected larvae by the number of positivated breeding places, is an inable index for representation of the breeding places potencialities of those anophelines. The fourth stage larvae average, from positive breeding places, has revealed to be a better index. Its annual circle curve is approximately parallel to that of the biomass and so, the author suggests for news works, the computation solely of the young forms of advanced stages.