The effect of mexidol administered in a dose of 100 mg/kg (i.p.) was studied in BALB/C and C57BL/6 mice on various emotional stress models including open field test, elevated plus-maze test, and passive avoidance conditioned reflex. Upon a single administration, the drug produces a selective anxiolytic action on BALB/C mice (experimental animals with a "passive" phenotype of the emotional stress reaction), while not inducing any sedative (tranquilizer) effect in C57BL/6 mice (belonging to the phenotype with "active" emotional stress reaction).