Additional Study Information: In the U.S., 82% of older adults test positive for antibodies to the herpes viruses. Basic and clinical evidence point to the herpes viruses as a possible cause or contributor to Alzheimer's disease. The long-standing theory that viruses may cause Alzheimer's disease has never been tested in a clinical trial. Anti-viral therapy in Alzheimer's disease will investigate the efficacy of treating patients with mild Alzheimer's disease with the U.S.A marketed generic anti-viral drug Valtrex (valacyclovir). Valacyclovir at 2g to 4g per day, will be compared to matching placebo in the treatment of 130 mild AD patients (65 valacyclovir, 65 placebo) who test positive for herpes simplex virus-1 (HSV1) or HSV2. The study will be a randomized, double-blind, 18-month Phase II proof of concept trial.