Schistosomaisis afflicts more than 200 million people worldwide. It is caused by copulating pairs of male and female blood flukes living in the veins of man and animals. The highly folded surface integument of male and female schistosomes has previously hampered studies of surface membrane phenomena in isolated males and females because test material may passively sequester in these irregular surfaces. We developed a simultaneous, triple isotope method for studies of individual male and female schistosomes. This provides a precise and reproducible estimation of permeability, the Tissue Uptake Index (TUI). It is the purpose of this study to investigate sex-specific permeability phenomena in male vs. female schistosomes, and also to examine metabolic interactions between the male and female partners. The use of this technology has established that the copulating (paired) male and female schistosome apparently exhibit surface permeabilities to hexoses which are quite dissimilar from separated (non-copulating) pairs. These studies will be extended to include compounds such as amino acids, nucleic acid precursors and amines, to determine the effect of the male upon surface permeability in the female, and vice versa. A major finding during the initial period of support was the demonstration that male schistosomes transferred glucose to the copulating female partner. The present investigations will define which are transferred between the copulating schistosome pair, i.e. male-female (or female-male) transfers, and whether specific biological functions necesssary to the survival of the pair are carried out solely (or primarily) by either the male or female. The effect of specific antibody fractions upon metabolite permeability will be compared in male vs. female schistosomes. The binding of radiolabeled antischistosomal serum fractions will also be compared in males and females. These studies are designed to characterize the metabolic interaction which occurs between the pair, and to ascertain whether or not this interaction is a potentially vulnerable site to antibodies (and in the future, to pharmacological attack).