The concept of hypoglycemia-associated autonomic failure (HAAF) in diabetes posits that recent antecedent iatrogenic hypoglycemia causes both defective glucose counterregulation (by reducing the epinephrine response in the setting of an absent glucagon response) and hypoglycemia unawareness (by reducing the autonomic-sympathetic neural and adrenomedullary response and the resulting neurogenic [autonomic] symptom responses) and thus causes a vicious cycle of recurrent hypoglycemia. To assess the suggestion that it is the cortisol response to antecedent hypoglycemia that mediates HAAF, we tested the hypothesis that plasma cortisol elevations during euglycemia that are comparable to those that occur during hypoglycemia reduce sympathoadrenal and neurogenic symptom responses to subsequent hypoglycemia. To do this, 12 healthy subjects were studied with hyperinsulinemic-stepped hypoglycemic clamps the day after saline or cortisol (1.3 ± 0.2 μg · kg⁻¹ · min⁻¹) infusions from 0930 to 1200 and from 1330 to 1600. Compared with saline, antecedent cortisol elevations did not reduce the sympathoadrenal (e.g., final plasma epinephrine levels of 674 ± 84 vs. 606 ± 80 pg/ml and final plasma norepinephrine levels of 332 ± 26 vs. 304 ± 26 pg/ml) or neurogenic symptom (e.g., final scores of 9.3 ± 1.1 vs. 13.2 ± 1.3) responses to subsequent hypoglycemia. Thus, these data do not support the suggestion that cortisol mediates HAAF.