Hypertensive vascular disease was studied in acute experimental angiotensin induced hypertension. If the hypertension was induced in rats pretreated with injection of thoracic duct lymphocytes the quantity of the mononuclear inflammatory cellular reaction in the damaged arterioles was 2–9 times higher and more prolonged than in control rats. This difference in the cellular reaction is in agreement with the cellular reaction in cases of hypersensitivity of the delayed typ