The effects of prostaglandin E2 (PGE2) and indomethacin on the vascular reactivity to norepinephrine were tested in three different isolated rat vascular beds (mesenteric artery, hind limb and splenic artery) perfused with the Krebs bicarbonate solution. In these vascular beds PGE2 (0.1-64 ng/ml) or indomethacin (09.1-96 microgram/ml) in the perfusate did not change the basal pressure. In the mesenteric vascular bed and the hind limb, PGE2 dose-dependently potentiated the vascular response to norephinephrine, whereas PGE2 dose-dependently inhibited the vascular response to norepinephrine in the splenic artery. In these three vascular beds indomethacin in the perfusate dose-dependently attenuated the vascular response to norepinephrine. In the mesenteric artery and the hind limb PGE2 restored the effect of indomethacin, but in the splenic artery PGE2 did not restore the inhibitory effect of indomethacin. These results indicate that the modulating effect of exogenously administrated PGE2 on the vascular action to norepinephrine varies in different vascular beds. It is also suggested that the contribution of endogenous PGE2 synthesized in the vascular wall to the vascular reactivity to norepinephrine is, as well as the effect of exogenous PGE2, different in different vascular beds.