Alzheimer's Disease (AD), a slowly progressive neuropsychiatric illness, principally characterized by memory deficits, has become the fourth leading cause of death in developed nations. Since the patients with AD suffer from marked reduction of cholinergic neuronal function resulting in a deficiency in acetylcholine (ACh) concentration in the brain, and these reductions are associated with impairments in memory, cholinergic enhancement strategies have been at the forefront of efforts to palliate pharmacologically the cognitive symptoms. Therefore, treatment approaches have been focused on the acetylcholinesterase inhibitors (AChEI) which are the most promising drugs demonstrating efficacy in the treatment of AD. Since, recently, galanthamine, an alkaloid isolated from different Galanthus species (Amaryllidaceae), has been found to be a potent and reversible acety1cholinesterase inhibitor, this development has prompted us to investigate the anticholinesterase activity in other plant species of Amaryllidaceae growing in Turkey, namely Galanthus elwesii, G. ikariae, Narcissus tazetta subsp. tazetta, Leucojum aestivum and Pancratium maritimum by Ellman method in comparison with galanthamine as the standard drug. Bioactivity-directed fractionation and kL isolation studies carried out on G. ikariae and N. tazetta subsp. tazetta extracts afforded 8 Amaryllidaceae-type alkaloids in total. We found that the activity of both of the plant extracts was due to the synergistic interaction of the alkaloids isolated.