Percentage water (42.8–97.57), total nitrogen (0·33–11·99) and calorific values (0·502–7·538 K. Cal/g dry weight) of entire organisms of 22 species from a tropical freshwater community were measured on the basis of dry weights. The values determined were found to bear no relation to the nature of food, physical habitat, size of the species, larvalstages or taxonomic position but may be associated with the ratio of inert to labile matter. For most of the organisms these values compared favourably with those of temperate forms.The high calorific value recorded for Branchiodrilus semperi was associated with high rate of asexual reproduction.