(-)-Epigallocatechin gallate (EGCG), a flavonoid, is the principal catechin found in green tea and is distributed in the brain after tea consumption. The aim of the present study was to investigate the effects of EGCG in the chick brain under an acute stressful condition and to clarify the mechanism by which EGCG attenuates stress behavior with special reference to gamma-aminobutyric acid (GABA). Intracerebroventricular (i.c.v.) injection of EGCG (50, 100 and 200 microg) suppressed the vocalization which normally occurs during social separation stress. EGCG decreased the time spent in active wakefulness and induced sleep-like behavior in a dose-dependent manner. Additionally, i.c.v. injection of EGCG attenuated plasma corticosterone release under social separation stress. These effects of EGCG on distress-induced vocalization were significantly attenuated by the GABAA receptor antagonist picrotoxin but not by the GABAB receptor antagonist CGP 54626 (3-N-(1-(3,4-dichlorophenyl)ethylamino)-2-hydroxypropyl cyclohexylmethyl phosphinic acid hydrochloride). These results indicate that EGCG has sedative and hypnotic effects in the brain, partially through GABAA receptors, and consequently moderates an acute stress response.