Young (5 month) and aged (23 month) male rats were tested in delayed nonmatching to position task using a T-maze, and their ability of working memory retention was assessed over interrun intervals ranging between 5 and 300 sec. There were no significant age differences in pretest performance at 0 sec interval, but significant memory loss was observed in aged rats when tested with the interrun intervals. Physostigmine (0.1 and 0.2 mg/kg) improved this age-related decline in working memory in a dose-dependent manner, whereas the treatment slightly but not significantly improved the performance of young rats. These results suggest that the central cholinergic system in aged rats was functionally deteriorated and that stimulation of the system could enhance working memory retention in aged rats.