The effects of combined hyperglycemia-hyperinsulinemia on whole body, splanchnic, and leg fatty acid metabolism were determined in five volunteers. Catheters were placed in a femoral artery and vein and a hepatic vein. U-¹³C-labeled fatty acids were infused, once in the basal state and, on a different occasion, during infusion of dextrose (clamp; arterial glucose 8.8 ± 0.5 mmol/l). Lipids and heparin were infused together with the dextrose to maintain plasma fatty acid concentrations at basal levels. Fatty acid availability in plasma and fatty acid uptake across the splanchnic region and the leg were similar during the basal and clamp experiments. Dextrose infusion decreased fatty acid oxidation by 51.8% (whole body), 47.4% (splanchnic), and 64.3% (leg). Similarly, the percent fatty acid uptake oxidized decreased at the whole body level (53 to 29%), across the splanchnic region (30 to 13%), and in the leg (48 to 22%) during the clamp. We conclude that, in healthy men, combined hyperglycemia-hyperinsulinemia inhibits fatty acid oxidation to a similar extent at the whole body level, across the leg, and across the splanchnic region, even when fatty acid availability is constant.