Unilateral family therapy is presented as a new mode of family therapy in which intervention is directed toward changing the behavior of an uncooperative family member through working with a cooperative member as mediator. In this initial exposition of the unilateral approach, it is applied to the problem of endeavoring to reach and change an uncooperative alcohol abuser through giving therapeutic assistance to a cooperating spouse. A working conception of this mode of therapy is presented based upon the authors' current clinical research in this area. Directions for further research and development are identified.