1. Men or women of non-childbearing potential, 55 years of age or older with a probable diagnosis of Alzheimer's Disease (AD), according to the National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) criteria. Subjects will have AD that is mild to moderate in severity, as qualified by a score of 12 to 26 on the Mini-Mental State Examination (MMSE). Woman of non-childbearing potential must be either surgically sterile (hysterectomy and/or oophorectomy) or postmenopausal at least 1 year and must have a negative serum pregnancy test result within 48 hours before administration of test article. Sexually active men must agree to use a medically acceptable form of contraception during the study and continue it for 12 weeks after test article administration.