This paper deals with the water balance of Guarea trichilioides L., a meliaceous tree, native in the tropical America. Transpiration was measured by the method of rapid weighing of detached leaflets. Determinations of transpiration values showed that G. trichilioides did'nt restrict transpiration in the more hot hours of the day. Relative transpiration was higher than that of the trees of the rain tropical forest. Relative cuticular transpiration was low, as in most trees of the rain forest, and lower than that of several plants of the cerrados (brazilian savannae). Hydroactive movement of the stomata was relatively rapid in the initial phasis, becoming however, very slow, before attaining the values of the cuticular transpiration. The saturation deficit was always low, as in the rain tropical forest trees. From the study of the water balance and leaf structure, we can realize that Guapea trichilioides is a tree of the tropical forest unadapted to support conditions of intense drought.