Competition studies and column chromatography demonstrated that adults Schistosoma mansoni contains three nucleoside kinases that can phosphorylate pyrimidine nucleosides; a non-specific deoxyriboside kinase (EC 126.96.36.199), a specific uridine kinase and a specific cytidine kinase. The non-specific deoxyriboside kinase can phosphorylate all naturally occurring pyrimidine and purine 2′-deoxyribosides. Uridine and cytidine kinases are specific for uridine and cytidine, respectively. Various nucleoside 5′-triphosphate act as phosphate donors for the three kinases albeit to different degrees. Nucleoside kinases are critical in the activation of potential anti-parasitic drugs which may be identified among the numerous available pyrimidine nucleoside analogues. The finding that S. mansoni have nucleoside kinases that differ from their host enzymes raises the possibilities that certain pyrimidine nucleoside analogues could be selectively toxic to schistosomes. © 2014 Elsevier B.V.