Abstract: Effects of melatonin on acute toxicity of ethanol and ethanol-induced hypothermia, ethanol and thiopental sleeping time and ethanol-induced hypermotility were investigated in mice. The melatonin (1 and 5 mg/kg) was injected i.p. in single or repeated doses (7 days). The experiments were performed during the light phase of the light/dark cycle. It has been shown that a single dose of melatonin shortened duration of ethanol sleep and decreased ethanol-induced hyperactivity in mice. Melatonin given to mice for 7 days did not influence ethanol-induced effects. Melatonin prolonged thiopental hypnotic effect. The results of central interaction of ethanol and melatonin may be of antagonistic or synergistic nature.