While an activation of the opioid system has been found to play a role only in the triggering of the high blood pressure induced by brief (7-14 days) social deprivation stress in Wistar rats, factors responsible for the maintenance of the hypertension after long-term (30-35 days) isolation remained to be elucidated. To this aim, the effects of social deprivation stress on the functional and morphological features of blood vessels were studied. The tail artery, as a muscular vessel, and the aorta, as a large elastic vessel were used in these experiments. In ex vivo experiments, aorta and tail artery strips from rats isolated for 30-35 days were found to be hyperreactive to noradrenaline.