It has been generally assumed that counterregulatory hormone responses to hypoglycemia are not influenced by gender. To test this assumption, we analyzed three separate hypoglycemic insulin clamp studies in age-matched, healthy, non-obese females (n = 33) and males (n = 37). In one study (12 females, 17 males), plasma glucose level was rapidly decreased to about 57 mg/dL for 100 minutes with a 0.65-mU/kg/min insulin infusion. Despite an identical decrease in glucose level, the increase in epinephrine (361 ± 64 v 188 ± 38 pg/mL, P < .05), norepinephrine (132 ± 28 v 47 ± 19 pg/mL, P < .01), and growth hormone ([GH] 16.0 ± 3.8 v 4.9 ± 1.9 ng/mL, P < .05) levels, but not glucagon or cortisol levels, were significantly greater in males than in females, respectively. In the second study (10 females, eight males), a 5.0-mU/kg/min insulin infusion was used to decrease glucose levels to 55 mg/dL for 180 minutes. Epinephrine (P < .05) and GH (P < .01) responses were greater in males than in females. In a third study (11 females, 12 males), plasma glucose level was gradually decreased to about 50 mg/dL over 240 minutes. Again epinephrine (P < .01), norepinephrine (P < .01), GH (P < .05), and cortisol (P < .01) responses were nearly twofold greater in males (P < .01). Multivariate analysis of all 70 subjects identified gender as the most significant factor contributing to the epinephrine (P < .001) and norepinephrine (P < .005) responses, and also as a significant contributor to the GH response (P < .05). Moreover, the glucose levels that triggered an increase in epinephrine, norepinephrine, and cortisol were each about 9 mg/dL higher in males (P < .05). We conclude that, with respect to males, females have decreased counterregulatory hormonal responses to hypoglycemia. This sexual dimorphism may be in part due to an alteration in the glucose threshold for hormone release.