Selenium compounds display antioxidant and neuroprotective properties. Diphenyl diselenide (PhSe)(2) is an organic selenium compound that affects a number of neuronal processes. The aim of the present study was to evaluate the effects of the systemic administration of (PhSe)(2) on novel object recognition memory in mice. Adult male CF1 mice were given an i.p. injection of (PhSe)(2) (0.2, 1.0, 5.0, or 25.0 micromol/kg) 30 min before training in an object recognition task. (PhSe)(2) did not affect short-term memory or the total time exploring both objects, but induced a facilitation of retention measured 24 h after training. The present findings show that systemic administration of (PhSe)(2) induces a facilitation of formation of long-term object recognition memory.