The authors studied the effect of prostacycline and prostaglandins E2 and F2 alpha on the tonus of renal vessels of normotensive rats and rabbits, as well as on the noradrenalin action in the renal and lymph vessels of normotensive and spontaneously hypertensive rats. The effect of prostacycline and prostaglandin E2 proved to be dependent on the type of the animals: in rabbits they reduced, whereas in rats they increased renal perfusion pressure. Indomethacin reduced, while prostaglandin E2 restored the noradrenalin-induced pressor reaction in normotensive rats. In rats with spontaneous hypertension these effects were less pronounced. Prostaglandin F2 alpha increased the pressor effect of noradrenalin both in normotensive and in spontaneously hypertensive rats.