The plasma and erythrocyte concentrations of were measured simultaneously among nonpreg Oxypurines nant subjects and pregnant patients with and without toxemia. There was a two- to threefold increase in the intracellular Xanthine concentration of hypoxanthine and , whereas the plasma concentration of uric acid exceeded the erythrocyte level by tenfold. Both plasma and erythrocyte xypurines were elevated with pregnancy, especially with toxemias. Of the 6 toxemic patients studied comparing both the peripheral vein and the intervillous space oxypurine concentrations, only one case clearly demonstrated unusually elevated hypoxanthine in the intervillous space blood suggesting possible overproduction by the toxemic placenta. There were no marked changes in blood oxypurines with labor; the umbilical cord levels reflected the maternal concentration.