Monosialoganglioside GM1 (GM1) has been found to alleviate genetic and lesion-induced memory deficits. The purpose of this study was to investigate the effects of 7-day treatment with GM1 (50 mg/kg IP) on acquisition and retention performance of senescent rats in a passive avoidance situation. Saline-treated old rats showed a decreased performance in acquisition and retention tests as compared to saline-treated adult rats. GM1 improved both acquisition and retention performance of old animals, and there was no significant difference between GM1-treated old rats and saline-treated adult rats. These data suggest that GM1 treatment can improve memory deficits in intact senescent animals.