Glucose catabolism via glycolysis leads to the generation of considerable amounts of lactic acid in schistosomes which must be transported out of the cell to avoid poisoning metabolic pathways. Accumulation of lactic acid leads to a decrease in intracellular pH and cessation of glycolysis. Therefore, lactic acid must be efficiently eliminated if high rates of glycolysis are to be maintained. It has been Garcinone-D estimated that as much as 0.043 mmol lactate/mg dry weight/hour is released by adult parasites cultured in medium containing 10 mM glucose. The molecular mechanisms by which schistosomes rid themselves of this lactic acid are not known. In some systems, lactic acid transport is carried out by a family of proton-linked monocarboxylate transporters located at the plasma membrane. Several MCT and MCT-related genes have so far been identified in mammals, each having a different tissue distribution. MCT genes have also been identified in other organisms of diverse phylogeny including Saccharomyces cerevisiae, Plasmodium falciparum, Drosophila melanogaster and Caenorhabditis elegans. We have examined the literature for reports of the presence of MCT homologs expressed in the tegumental membranes of intravascular schistosomes, through which lactic acid might be exported from the worms, and we failed to identify such molecules. In our ongoing characterization of the schistosome hostinteractive tegument, we cloned and characterized a cDNA encoding an aquaporin protein which we designated SmAQP. Proteomic analysis of isolated tegumental membranes had earlier shown that the protein was localized there. SmAQP is a 304 amino acid membrane protein that is most highly expressed in the intravascular life stages. RNA interference experiments in which SmAQP gene 7-O-ethyl-morroniside expression was suppressed in the schistosomula life stage revealed that the protein was important for the control of water movement into and out of the parasites. SmAQP-suppressed schistosomula exhibited lower viability in culture relative to control parasites and SmAQP-suppressed schistosomes had a generally more stunted appearance.