Development for the treatment of Alzheimer's disease. Alzheimer's disease (AD) represents a multifactorial disorder involving multisystemic factors in the CNS, characterized by cognitive and behavioral abnormalities. The most relevant pathogenic events in AD can be classified into four main categories: primary events (genetic factors, neuronal apoptosis), secondary events (b-amyloid deposition in senile plaques and brain vessels, neurofibrillary tangles due to hyperphosphorylation or tprotein, synaptic loss), tertiary events (neurotransmitter defects, neurotropic alterations, neuroimmune dysfunction, neuroinflammatory reactions) and quaternary events (excitotoxic reactions, calcium homeostasis miscarriage, free radical formation, primary and/or reactive cerebrovascular dysfunction). All of these pathogenic events are potential candidate targets for AD treatment and drug development. Central cholinergic systems have been repeatedly shown to play an important role in learnig and memo. Antycholinesterase (AChE) inhibition is presently the most successful method to ameliorate cholinergic deficit and lead to symptomatic improvement. These include drugs n tacrine, rivastygmine, donepezil, galantamine, and new AChE inhibityors such as phenserine, huperzine A, metrifonat, zanapezil are in clinical trials as a potential treatment of Alzheimer's disease.