A Dose Ranging Study To Investigate The Efficacy And Safety Of SB-742457 In Alzheimer's Disease

Inclusion criteria: * Clinical diagnosis of probable mild-to-moderate Alzheimer's disease as determined by the NINCDS-ADRDA and DSM-IV criteria with an MMSE score of 12-24. * Subjects and their caregivers must provide informed consent prior to study entry. * Adequate blood pressure and laboratory values. Exclusion criteria: * Females of child-bearing potential. * Have other causes of dementia such as vascular damage, depression, bipolar affective disorder, schizophrenia, syphilis, vitamin B12 deficiency or thyroid deficiency. * Subjects taking medication for Alzheimer's disease or centrally acting agents which might impact study outcomes. * Subjects taking agents for which there is a theoretical risk of interaction with SB-742457. * Subjects with known hypersensitivity to sunlight or seizures.