In a tropical rain forest near San Carlos de Rio Negro, Venezuela, average yearly precipitation from September 1, 1975, through August 31, 1977 was 3664 mm. Throughfall was 87% of precipitation, stem flow was 8%, transpiration was 47%, evaporation from leaf surfaces was 5%, and sub-surface runoff was 48%. These results conform closely to the prediction of Marques et al. (1977) that 48% of the precipitation that falls on the central Amazon Basin is derived from evapotranspiration within the Basin.