To test whether oral carbohydrate would provide greater conservation of body protein than would intravenous carbohydrate, healthy normal human subjects were infused with high doses of glucose either continuously intravenously or by nasogastric tube in both continuous and intermittent regimes. Metabolic responses to high calorie, nitrogen-free infusions in normal man were documented in the blood hormone and substrate changes, and protein sparing was assessed by urinary nitrogen excretion. Continuous glucose produced a lower urinary "nitrogen floor" than did the intermittent regime, and intravenous glucose was more effective than was oral glucose. The insulin responses to continuous nasogastric and continuous intravenous glucose were similar, and nitrogen excretion did not differ between those two groups. The increased insulin levels seen with intermittent glucose were not accompanied by greater protein sparing.