The author presents a rapid introduction in which the present study is situated in the program of work of the Instituto de Malariologia, in the southern litoral of Brazil. Then, with the help of a series of graphs, he shows, the distribution of air temperature, relative humidity and evaporation, in three zonations and between the various synusiae of the forest. Besides the monthly averages and totals, the data for daily and nightly observations are presented. This will make it possible for other workers to study possible correlations between these data and mosquito behaviour. Based on the graphs presented the author reaches, among others the following conclusions: 1. Air temperature: Generally, in the forest, the mean temperature is lower than in the open. However, in the winter, chiefly in the months of clear sky, when the outgoing radiation is very intense, the reciprocal may also be observed. The values obtained in the various zones at the same height, were, in the summer, almost the same, with slight tendency to normal stratification. On the other hand, in winter the averages were affected by nocturnal inversion of temperature and showed greater differences. in a same zone the averages were always greater inthe upper layers than in the lower ones. 2. Relative humidity: The averages obtained in the forest, in dependency of the place, were higher or lower than in the open air. Between the same layers of vegetation the values were always higher in the valley, lower on the top of the hill and intermediate in the middle of the slope of the mountain. In each zone the averages were always lower near the crown of the trees than under the shrubs. The nocturnal inversion of temperature has little effect over the distribution of the mean values of relative humidity. 3. Evaporation: During the day, evaporation is higher in the open air than under the shrubs of the forest, a condition which is not always prevalent at night. Among the zones, the top of the elevation...