The author emphasizes that dual-diagnosis patients are a complex and difficult group to treat. They are often misdiagnosed, undertreated, or shifted between mental health and chemical dependency treatment units. The discussion of depression covers its association with alcohol and both pharmacotherapy and group therapy for depressed alcoholics. Relationships between depression and opiates and nonopiates are explored. Sections on sociopathy and schizophrenia follow a similar outline, noting links between substance abuse and these mental disorders. A profile of a treatment program at St. Paul-Ramsey Medical Center illustrates issues with which a treatment program for the dual-diagnosed client must deal. It emphasizes that mental health professionals and substance abuse counselors must be cross-trained, that treatment programs should be designed to meet multiple needs, and that professionals in the two fields must set aside their differences for the patient's benefit. Over 40 references.