The effects of several amino acids on isolated perfused adrenal glands of dogs were investigated. Methionine (5 x 10(-5)--5 x 10(-2) M), glutamic acid (5 x 10(-5--5 x 10(-2) M), glutamine (10(-4)--5 x 10(-2) M), serine (5 x 10(-4)--5 x 10(-2) M), cysteine (5 x 10(-4)--5 x 10(-2) M), arginine (10(-3)--5 x 10(-2) M), and threonine (5 x 10(-3)--5 x 10(-2) M) consistently increased the rate of release of catecholamine (CA) from the glands for about 8 min. Preinfusion with hexamethonium (C6, 10(-4) M) plus atropine (5 x 10(-5) M) reduced the effects of methionine and glutamic acid slightly, and it completely inhibited the effect of acetylcholine (ACh, 10(-6)--10(-3) M). Preinfusion of physostigmine did not significantly influence the effects of methionine, glutamic acid, cysteine, and serine. Ca2+ free perfusion fluid depressed or abolished the effects of amino acids. They had no effect on the release of CA from isolated chromaffin granules. It seems likely that amino acids depolarize chromaffin cells in the adrenals and release CA from its storage sites. The effects of these amino acids on adrenal medulla cannot involve release of ACh from splanchnic nerve endings.