Effects of ethanol and acetaldehyde on the release of arginine-vasopressin (AVP) and oxytocin (OXT) were examined using a superfusion system of the isolated hypothalamo-hypophyseal complex of rats. The release of both hormones was significantly suppressed by exposing the tissue samples to Eagle MEM medium containing 1.75 and 2.5% ethanol (the maximal suppression: AVP, 30% and 70%; OXT, 30% and 70%, respectively). However, perfusion with medium containing 3.75 and 5.0% ethanol enhanced the release of OXT during exposure to ethanol (the maximal increase, 1,000%) and the release of AVP was increased markedly just after exposure to ethanol was stopped (the maximal increase, 800%). Perfusion with medium containing 50, 100 and 250 microM acetaldehyde did not affect the release.