All studies were carried out with male Wistar rat. Blood samples were collected by decapitation. Plasma rat GH was measured by solid-phase radioimmunoassay technique. Tibia break and ether-laparotomy stress caused no significant change in plasma GH in urethane (150mg/100g B. W.)-pretreated rats. In pentobarbital (5mg/100g B. W.)-pretreated rats, on the other hand, tibia break resulted in a marked decrease (P<0.01) in plasma GH and etherlaparotomy stress produced a marked rise (P<0.01) in plasma GH. The intracarotid injectionof NIAMDD rat hypothalamic extract (the epuivalent of 2 rat median eminences) produced a significant rise (P<0.01) in plasma GH in urethane-pretreated rats, but by ether exposure prior to urethane ip injection, this significant rise of plasma GH was disappeared. In pentobarbital-pretreated rats, on the other hand, the intracarotid injection of rat hypothalamic extract produced a significant decrease (P<0.05) in plasma GH. These findings may suggest that NIAMDD rat hypothalamic extract has both GH-releasing and GH-inhibiting actions.