The effects of beta-selective blockade with metoprolol on the glucagon blood plasma level during insulin-induced hypoglycemia were studied in 20 control dogs, and 20 alloxan diabetic dogs. The results indicate that the sensitivity to exogenous insulin is increased in alloxan diabetes glucose counterregulatory mechanisms are impaired. After insulin administration glucagon concentration increased much more and quicker in the control group than in diabetic dogs. Beta-blockade with metoprolol increased glucagon secretion in both groups.