T he utilization of circulating maltose was compared to that of glucose in six normal fasting subjects after intravenous injection of 25 g of either sugar. Blood samples were obtained over a 2 hr period and were assayed for free fatty acids (FFA), insulin, glucose, and total reducing substances. Urine was collected for 2 hr after maltose administration and assayed enzymatically for glucose and maltose. Blood glucose concentrations did not increase after maltose infusion, although a significant rise in total reducing substances was noted, indicating the presence of this disaccharide in the blood. Less than 3% of the administered maltose was excreted in the urine either as maltose or glucose. Initially, there was a fourfold increase in serum insulin concentration after glucose and a threefold increase after maltose infusion. Therefore, serum insulin concentrations gradually declined in a similar manner for both sugars. The plasma FFA at 15 min decreased 371 uEq/liter after glucose and 338 uEq/liter after maltose infusion.In other studies, 10 g maltose containing 5 μCi maltose-U-¹⁴C were injected into five human subjects and expired CO₂ collected for 6 hr. Maximal ¹⁴CO₂ specific activity was noted at 170 min and a mean of 61.1% of the injected radioactivity was recovered as ¹⁴CO₂. Less than 8% of the injected ¹⁴C was excreted in the urine.These results indicate that maltose administered intravenously has similar metabolic effects when compared to glucose, and may be efficiently utilized as a carbohydrate substrate. The oxidation of intravenously administered maltose-U¹⁴C to ¹⁴CO₂ demonstrates that circulating maltose is readily metabolized. A solution of maltose could provide twice the mass of sugar (and of calories) per milliliter as an equimolar solution of glucose. Parenterally administered maltose may be of clinical value and should be further studied.