The primed constant infusion of glucose-2−3H was used to study the influence of prostaglandins (PGs) infusion (2μg./min.) on glucose turnover in intact rats in the postabsorptive state. While PGA1 did not exert any appreciable effect on glucose production by the liver and on plasma glucose levels, prostaglandins of E-series significantly increased hepatic glucose output and consequently plasma glucose levels. In this regard, PGE1 appeared more effective than PGE2. In some experiments PGE1 was infused for two hours at the dose of 1.5μg./xmin.: glucose concentration rose to a maximum of 127 per cent above the control values and glucose production reached during the second hour of the infusion a level twice the base line (from 8.1 ±0.5 to 16.9±0.5 mg./kg. body weight/min.). These changes were paralleled by a proportional increase in glucose uptake by peripheral tissues which reached a level very near to that of hepatic output toward the end of the infusion.