Direct sleep-inducing test in rabbits and mice and the test of sleep-inducing in coordination with pentobarbitone(PBB) and barbital(BB) in mece were described to examine the effect of Melatonin on sleep. The results indicated that Melatonin had no direct sleep-inducing effect on mice even at high dose of 1.00 g/kg BW(ig), but it did on rabbits at dose of 20 mg/kg BW(ig). Melatonin potentiated PBB-inducing sleep with the ED 50 7.03 mg/kg BW(male), 19.05 mg/kg BW(female), and it could shorten the falling asleep time in coordination with BB. Author's address Zhong Weijian, Health and Anti-epidemic Station of Shanghai city, 200335 PRC.