When rats were exposed to immobilized cold stress, adrenaline content in the adrenal gland as well as noradrenaline content in the brain stem were reduced drastically, while noradrenaline content in the atria was not altered by the application of stress. Oral administrations of taurine (4-7 g/kg/day, for 3 days) prevented the stress-induced decline of adrenaline in the adrenal gland and this preventive effect could not be duplicated by the administration of L-isoleucine or DL-methionine. In hypophysectomized rats, the stress also induced a significant fall in adrenaline content of the adrenal gland, however taurine administration did not show significant preventive effects on the decline in adrenal catecholamines. The immobilized cold stress induced a significant increase in blood sugar and this increase was antagonized by pretreatment with taurine. Taurine had no significant effects on the stress-induced increase in the activity of adrenal tyrosine hydroxylase and the turnover rate of adrenaline in the adrenal gland measured by the rate of decline of this amine following α-methyl-tyrosine administration. The administration of taurine, in both in vivo and in vitro, inhibited the release of adrenaline from adrenal medullary granules, but that of dopamine-β-hydroxylase was not significantly affected. The stress-induced elevation of the blood level of corticosterone was not affected by taurine administration. These findings indicate that taurine antagonizes the stress-induced elevation of blood sugar by reducing adrenaline output from the adrenal gland. The regulatory mechanism most likely involves the inhibition of adrenaline release from adrenal medullary granules, possibly by stabilizing the membrane of the granules.