Major depression is thought to be underdiagnosed and undertreated in primary medical care facilities. The authors conducted a clinical trial that included a three-phase assessment so only ambulatory medical patients judged eligible for treatment of this disorder in medical settings were recruited. In addition to administering the Center for Epidemiologic Studies-Depression scale and the Diagnostic Interview Schedule's (DIS) Depression section, the psychiatrists evaluated the DIS-positive patients. This third assessment determined that clinical characteristics of DIS-positive patients were such that 70% of the patients could be treated for major depression in a primary care setting, 13% should probably be referred to a mental health facility, and 17% were experiencing conditions other than major depression.