Animal experiments indicate that the kidney may play an important role in glucose counterregulation. Because the human kidney normally takes up and releases glucose, and since patients with end-stage renal disease are prone to hypoglycemia, we examined whether the kidney is also involved in human glucose counterregulation. Accordingly, we compared renal glucose release (RGR) and uptake (RGU) during 4-h hyperinsulinemic-hypoglycemic (approximately 3.2 mmol/l, n = 9) and -euglycemic (approximately 5 mmol/l, n = 10) control clamp experiments in normal postabsorptive subjects. A combination of renal balance and isotopic ([3H]glucose, [14C]glutamine) techniques was used, which permitted hepatic glucose release (HGR) and glutamine gluconeogenesis to be calculated as the difference between systemic (overall) and renal values. In both experiments, infusion of insulin increased plasma insulin comparably (approximately 210 pmol/l). In euglycemic control experiments, RGR and HGR decreased more than 50% (both P<0.001) and RGU increased approximately 35% (P = 0.02). In hypoglycemic experiments, both HGR (P = 0.034) and RGR (P<0.001) increased to a comparable extent (1.69+/-0.47 and 1.67+/-0.15 pmol x kg-(-1) x min(-1), respectively, P = 0.96) above rates observed in control experiments; hepatic and renal glutamine gluconeogenesis increased by 0.19+/-0.06 (P<0.008) and 0.30+/-0.07 pmol x kg(-1) x min(-1) (P< 0.001), respectively. RGU decreased by 65% compared with control experiments (P<0.001), so that renal glucose balance changed from a net uptake of 80+/-19 micromol/min to a net release of 130+/-9 micromol/min, P< 0.001. These observations provide evidence that the kidney may play an important role in human glucose counterregulation.