Short-term in vitro pulse-labeling of the free glucose pool in pairs of Schistosoma mansoni, and measurement of the increase in [14C]glucose in the female partner (and the concomitant decrease in the male), has established that glucose can be transferred from male to female schistosomes. It is demonstrated that this transfer is not inhibited by ouabain in S. mansoni. Free glucose levels have been measured in Schistosoma haematobium, Schistosoma japonicum and S. mansoni. Data indicate that the transfer of glucose is not via an active mechanism, but rather the transfer of glucose occurs along a glucose concentration gradient which exists between males and females.