This article discusses the role of correctional line staff in treatment of prison inmates with serious mental illness. The authors assert that many roles and duties traditionally attributed to clinicians can and often should be performed not only by mental health professionals, but by line staff such as correctional officers and nurses. Moreover, the optimal climate for effective treatment is one in which mental health professionals and line staff work collaboratively, especially since line staff alone are in contact with inmates 24 hours per day. The specific activities which comprise mental health treatment in prison are described as: 1) counseling and psychotherapy-talking with inmates, 2) consultation-talking about inmates, 3) special housing, activities, and behavioral programs, and 4) medication. Case examples demonstrate how correctional officers, nurses, and other line staff perform each of these activities. Recognition and nurturance of these activities will improve the quality of services and reduce stress on staff and inmates alike. Consultation with line staff, joint training, and use of multi-disciplinary treatment teams are advocated as methods of reaching these goals.