The purpose of this protocol is to utilize Tacrine (1,2,3,4 - tetrahydro-9-aminoacridine, monohydrochloride monohydrate, CI-970) in a double-blind, placebo controlled study to test the efficacy of the drug in senile dementia of the Alzheimer's type. Tacrine is a potent, centrally active, reversible cholinesterase inhibitor.