In this paper we describe the effect of poly-L-lysines of different molecular weight on the schistosomula. In the control sample, the schistosomula of Schistosoma mansoni take up fluorescent Texas Red conjugated to bovine serum albumin (TxR–BSA) into the gut. Following slight damage by 24·0 kDa poly-L-lysine, a high proportion of schistosomula take up fluorescent TxR–BSA into the excretory system. Subsequently, the dye diffused into the bodies of the schistosomula. We suspected that this diffusion involved the process of endocytosis so we investigated this with the use of endocytosis inhibitor, Latrunculin A. Addition of the endocytosis inhibitor Latrunculin A following poly-L-lysine treatment inhibited gut uptake of TxR–BSA as well as the diffusion of excretory-ingested TxR–BSA molecules.