The purpose of the study is to determine the safety, tolerability, and efficacy of 3 doses of lecozotan in combination with a cholinesterase inhibitor in patients with mild to moderate Alzheimer's disease (AD).

Inclusion Criteria:

• Diagnosis of probable Alzheimer's disease
• Current use of cholinesterase inhibitor
• Able to give signed and dated informed consent and lives with appropriate caregiver at home or in community dwelling with caregiver accompanying patient to all visits and visiting patient at least daily for duration of the study

Exclusion Criteria:

• Significant neurological disease other than AD
• Diagnosis of major depression
• History of stroke or other heart disease