Chronic treatment of rats with 90 microg/kg/day DPSPX (1,3-dipropyl-8-sulphophenylxanthine) during seven days leads to a hypertensive state which is characterized by marked morphological changes of the blood vessel walls as well as by important functional alterations. While the angiotensin-converting enzyme (ACE) inhibitor captopril and the antagonist of angiotensin II AT 1 receptors losartan prevent the development of both hypertension and morphological changes, the selective beta1-adrenoceptor antagonist atenolol could prevent only the increase in blood pressure. It is concluded that at least two factors are involved in the development of the hypertensive state.