The document presents Maine's model for providing substance abuse treatment to the client with mental retardation. Introductory information on retardation and substance abuse is followed by a discussion of this population's unique problems. Services offered in the Mental Retardation Alcoholism project are reviewed, and contracts and cooperative service aggreements are viewed as approaches to improve interagency relationships. Staff training programs are outlined, including guidelines for assessment, treatment, and aftercare. Case studies illustrate the joint planning process and possible outcomes of intervention. Extensive appended material is organized according to material for the system (such as service contracts), assessment process (including the interviewing questionnaire), and treatment and aftercare (including guidelines to behavior modification and educational consideration). (CL)