It has been known that, during hypoxia, the adrenal medulla is activated to release catecholamines (CA) while hypoxia also inhibits high K⁺ -induced CA secretion in the cultured bovine adrenal chromaffin cells. The present study was attempted to examine the effect of hypoxia on CA secretion evoked by chlinergic stimulation and membrane-depolarization from the isolated perfused rat adrenal glands and also to clarify its mechanism of action. For this purpose, using the isolated rat adrenal glands, the effects of hypoxia on CA release evoked by nicotinic (N₁) and muscarinic (M₁) receptor agonists, membrane-depolarizing agent, Ca⁺⁺-channel activator, intracellular Ca⁺⁺-releaser and ACh were determined. Experiments were carried out, perfusing Krebs solution pre-equilibrated with a gas mixture of 95% N₂ and 5% CO₂. Hypoxia was maintained for 3 ~ 4 hours through the experiments. Hypoxia gradually caused a time-dependent seduction in CA secretion evoked by DMPP (100μM), McN-A-343 (100μM), ACh (5.32 mM), Bay-K-8644 (10μM) and high K⁺ (56 mM) respectively. How-ever, it did not affect CA secretion evoked by cyclopiazonic acid (10μM). Hypoxia itself also did fail to produce any influence on spontaneous secretory response of CA. These experimental results suggest that hypoxia depresses CA release evoked by both cholinergic stimulation and membrane-depolarization from the isolated rat adrenal medulla, and that this inhibitory activity may be due to the result of the direct inhibition of Ca⁺⁺ influx into the chromaffin cells without any effect on the calcium mobilization from the intracellular store.