Xylazine (rompun) has sedative, analgetic and myorelaxative effects; in addition to this, it also influences the homeostasis of glucose in the organism. The changes in glucose tolerance were studied in young rats after the administration of xylazine in combination with the blockers of adrenergic receptors. Xylazine caused hyperglycaemia and glucose intolerance in young rats and the administration of the beta-adrenergic blocker (propranolol) prolonged this diabetogenic effect. On the other hand, glucose tolerance after the administration of xylazine with alpha-adrenergic blocker (phentolamine) is close to the normal level. It is supposed on the basis of our results that xylazine-induced glucose intolerance and hyperglycaemia are mediated by the stimulation of the alpha-adrenergic system. Besides inhibition of insulin secretion, hepatic glycogenolysis probably also increases.