Victims of senile dementia will increase undoubtedly with increase of the aged population, and more than 90% of senile dementia are brain organic disordors that is, cerebrovascular dementia and neurodegenerative disorders. Drugs, now in use, are cerebral vasodilators, cerebral metabolism enhancers or drugs which modify the neurotransmission in the brain, however, these drugs do net directly cure the dementia itself, but only improve the surrou nding symptoms. Therefore, development of drugs for the treatment of senile dementia is the most urgent problem. In Chinese medicine, many prescriptions which are effective on the symptoms of “senile dementia" have been invented, and new prescriptions are still developing. Among the crude drugs recorded in Chinese medical plants dictionary “Zhong yao da cidian,” Ginseng, Acorus, Polygala, Epimedium, Longan, etc. are described as effective on amnesia and/or “trance”in their chief indications. Then, how can we develop the crude drug prescription and crude drug constituents as drugs for prevention or treatment of senile dementia, i.e. dementia caused by brain organic disorders?. In this presentation, I introduce effect of crude drugs or their main components on senile dementia which are under investigation in my laboratory with the following screening methods. 1. Development of memory impairment induced by drugs, electroshock (ES) or hanging stress. 1) Scopolamine- and alcohol-induced memory acquisition impairment, ES-induced memory consolidation impairment, and alcohol-and ES-induced memory retrieval impairment 2) Hanging stress-induced memory retrieval impairment. 2. Method using animal model, 1) Learning and memory deterioration of senescence accelerated mouse (SAM) P-8 2) Learning and memory deterioration of basal forebrain electrolytically lesioned mouse.