The effect of intracerebroventricular (i.c.v.) administration of magnesium on calcium- and dopamine-dependent brain function was investigated behaviorally and biochemically. The duration of ethanol-induced sleeping time in mice was prolonged following i.c.v. administration of calcium chloride (10 micromol/kg) or dopamine (30nmol/mouse); however, it was not affected by magnesium chloride (10 or 40 micromol/kg). The ability of calcium to prolong ethanol-induced sleeping time was inhibited by the administration of magnesium chloride. The brain dopamine level in mice was significantly increased following i.c.v. administration of calcium chloride. Taking into consideration these results and those from previous studies, it is suggested that calcium enhances dopamine synthesis in the brain through a calmodulin-dependent system, and the increase in dopamine level prolongs ethanol-induced sleeping time. However, magnesium inhibits dopamine release. Therefore, magnesium may inhibit calcium-dependent brain function through dopaminergic neurons, and consequently reduce the effect of calcium on ethanol activity.