Recently, we reported that intracerebroventricular (i.c.v.) injection of L-alanine attenuated the stress response under an acute stressful condition in chicks. However, no information of L-alanine was available for the influence on energy expenditure and changes in the posture under stressful conditions. The purpose of the present study was to clarify whether central L-alanine affects heat production (HP) of neonatal chicks, and whether HP is correlated with the behavior after isolation-induced stress. The i.c.v. injection of L-alanine (0.8 μmol) decreased oxygen consumption, carbon dioxide production and HP shortly after injection. Central L-alanine reduced the posture for active wakefulness, but increased the posture for sitting motionless with head drooped (sleeping posture). The present study demonstrates that central L-alanine decreases energy expenditure and causes a hypnotic effect in chicks exposed to an acute stressful condition.