The influence of naloxone on recovery from hemorrhagic hypotension was investigated in conscious normotensive and spontaneously hypertensive (SHR) Wistar-Kyoto rats. In both groups arterial blood pressure (MBP) was reduced to 50% of the resting level by arterial bleeding. Administration of naloxone (0.02 mg/kg iv) significantly impaired restitution of MBP in WKY and SHR in comparison to control experiments on WKY and SHR receiving no naloxone. The magnitude of this effect was similar in both strains, however in SHR, it appeared with a significant delay. The results indicate that small doses of naloxone may suppress recovery from hemorrhagic hypovolemia.