The present study was attempted to investigate the effect of strychnine on catecholamine (CA) secretion evoked by ACh, high K⁢, DMPP and McN-A-343 from the isolated perfused rat adrenal gland. The perfusion of strychnine (10⁣4 M) into an adrenal vein for 20 min produced great inhibition in CA secretory responses evoked by ACh (5.32⁓10⁣3 M), DMPP (10⁣4 M for 2 min) and McN-A-343 (10⁣4 M for 2 min), but did not alter CA secretion by high K⁢ (5.6⁓10⁣2 M). Strychnine itself did also fail to affect basal catecholamine output. Furthermore, in adrenal glands preloaded simultaneously with strychnine (10⁣4 M) and glycine (an agonist of glycinergic receptor, 10⁣4 M), CA secretory responses evoked by ACh, DMPP and McN-A-343 were considerably recovered to some extent when compared with those evoked by treatment with strychnine only. However, CA secretion by high K⁢ (5.6⁓10⁣2 M) was not affected. Taken together, these results demonstrate that strychnine inhibits greatly the CA secretory responses evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors, but does not affect that by membrane depolarization. It is suggested that strychnine-sensitive glycinergic receptors are localized in rat adrenal medullary chromaffin cells.