Plasma epinephrine, norepinephrine, and dopamine responses were studied in insulin-dependent diabetic patients at rest, on standing and during insulin-induced hypoglycemia. beta-Adrenergic sensitivity was evaluated by the isoproterenol sensitivity test. Five men who had adrenergic symptoms during hypoglycemia and no severe hypoglycemic accidents (coma, seizures) (group A) and five men who had repeated severe hypoglycemic accidents but lack of adrenergic symptoms of hypoglycemia (group B) were studied. The mean resting plasma epinephrine was lower in group B (147 +/- 22 pmol/L, SEM) than in group A (398 +/- 98 pmol/L, P less than 0.02). On standing plasma epinephrine increased significantly in both groups. During hypoglycemia blood glucose decreased identically in the two groups; plasma epinephrine and norepinephrine increased significantly and to the same extent in both groups; the mean maximal heart rate was significantly greater in group A than in group B. Isoproterenol sensitivity (defined as the dose of isoproterenol required to increase heart rate by 25 beats/min) was lower in group B (5.87 +/- 1.12 micrograms) than in group A (2.37 +/- 0.22 micrograms, P less than 0.01). The group B patients had significantly fewer hypoglycemic symptoms during insulin-induced hypoglycemia than did group A patients. We conclude that decreased beta-adrenergic sensitivity contributes to the lack of adrenergic symptoms of hypoglycemia in insulin-dependent diabetic patients.