An effect of the selective beta-adrenergic block with metoprolol and non-selective beta-adrenergic block with propranolol on the hypoglycaemia was investigated in 30 dogs of the control group and 30 dogs with alloxan diabetes. A significant increase in cortisol secretion was seen in the insulin-induced hypoglycaemia in both groups without beta-adrenergic block. It suggests an important role of cortisol in the normalization of glycaemia following an administration of the exogenous insulin. Beta-adrenergic block, especially with metoprolol, produces a significant increase in cortisol secretion confirming the report on direct effect of this beta-adrenolytic agent on cortisol secretion.