In mammalian brain, agmatine is an endogenous neurotransmitter and/or neuromodulator. In this study, the anxiolytic action of agmatine (p.o. or s.c.) was evaluated in three animal behavioral models in mice or rats. In the light-dark transition test, agmatine in a single dose (80 mg/kg, s.c) or repeated administration (20 mg/kg, s.c. or 10 mg/kg, p.o., once a day for 3 days) significantly increased the number of light-dark transitions in mice. Furthermore, treatment with agmatine (20-80 mg/kg, s.c or 10-40 mg/kg, p.o) three times in 24 h significantly increased the number of licks in the Vogel's drinking conflict test in rats. In the social interaction test, agmatine (10-40 mg/kg, p.o, three times in 24 h prior to test) increased the active social interaction of rats. All these results indicate that agmatine exerts a significant anxiolytic effect in both rats and mice.