Effect of tacrine, a cholinesterase inhibitor, on spatial acquisition deficit caused by permanent occlusion of bilateral common carotid arteries (2VO) was examined by using the conventional 8-arm and the 4-arm baited radial maze tasks in rats. Daily administration of tacrine (0.1 and 0.3 mg/kg, i.p.) 1 month after 2VO operation significantly improved the impaired spatial acquisition in the conventional maze task. This treatment also ameliorated the 2VO-induced working but not reference memory deficit in the 4-arm baited radial maze task. These results suggest that tacrine improvement of working memory deficit in the 2VO rats is due to stimulation of central cholinergic systems.