Study Comparing 3 Dosage Levels of SAM-531 in Outpatients With Mild to Moderate Alzheimer Disease.

The study will evaluate the efficacy and safety of an investigational drug called SAM-531 at
three dosage levels. Subjects will receive either SAM-531, donepezil or placebo for the
first 24 weeks of the study (period I). Subjects who receive placebo for period 1 will be
assigned to receive SAM-531 for the remaining 28 weeks of the study, while subjects who
received one of the three SAM-531 dosage levels or donepezil in period I will continue with
the same study drug (period II).