The study was performed on three groups, each including 10 male Wistar rats, weighing 110-130 g: group 1, the control group; group 2, animals treated with magnesium sulfate in a dose of 100 mg/kg body/day i.m.; group 3, animals treated with double dose of magnesium sulfate (200 mg/kg body/day i.m.). All animals were tested for emotivity and spontaneous motility in the open field, as well as for their capacity of acquiring active avoidance conditioned reflexes in the shuttle-box, for 9 days. Magnesium sulfate decreased significantly the learning ability, decreased emotivity scores regardless of the administered dose, and increased significantly spontaneous motility scores only in the double dose treated group.