This is a Study to Determine the Antidepressant Effects of AZD6765

An Investigation of the Antidepressant Effects of an NMDA Antagonist in Treatment-Resistant Major Depression

The purpose of this study is to determine the antidepressant effects of AZD6765 compared to placebo.

Inclusion Criteria:

• Patients with a diagnosis of Major Depressive Disorder, currently depressed without psychotic features
• Females must be of non-childbearing potential.

Exclusion Criteria:

• Treatment with Clozapine or ECT within 3 months prior to study
• Current or past history of psychotic features or a diagnosis of schizophrenia or any other psychotic disorder as defined in the DSM-IV