The tegument of Schistosoma mansoni contains a number of proteins that presumably function in its maintenance and/or repair against damage incurred from host-mediated humoral immune responses. Here, we show that the schistosome antigen identified by monoclonal antibody 709A2/2 is a cytoplasmic dynein light chain. Dynein light chains are components of dynein, an enzyme complex involved in various aspects of microtubule-based motility. Monoclonal antibody 709A2/2 recognizes two polypeptides, one of 8.9 kDa and a second of 7.6 kDa, as determined by SDS-polyacrylamide gel electrophoresis. We find that expression of S. mansoni dynein light chain is developmentally regulated and localized to the tegument in the schistosomula, lung stage worms, and adult worms, but is not present in the cercariae or ciliated miracidia. By Northern blot analysis of adult worm RNA, S. mansoni dynein light chain is encoded by a single message of ≃600 base pairs. A cDNA encoding this polypeptide contains an open reading frame of 89 amino acids with a deduced molecular mass of 10.4 kDa. Coprecipitation of an apparent 18.4-kDa antigen with S. mansoni dynein light chain by monoclonal antibody 709A2/2 illustrates that this molecule has an affinity for other proteins. Such interactions may play a role in S. mansoni dynein light chain participation in organelle trafficking in S. mansoni.