The fourth in a series on deinstitutionalization of individuals with developmental disabilities in Ohio, the paper concentrates on the contributions of formal and informal supports. Following a review of basic planning principles, formal support services necessary for planning community-based services for persons with developmental disabilities are listed, including transportation, service coordination, income maintenance and budgeting, mental and physical health services, and legal services. Possible problem areas facing systems shifting from a categorical to a generic resource based approach are noted. Informal supports, such as neighbor or family help, group religious activities, and neighborhood clubs are discussed, and their value to families with developmentally disabled members is emphasized. Obstacles to development of informal supports are noted, and the importance of helping disabled persons develop and maintain informal support relationships is underlined. A series of recommendations regarding formal and informal support systems concludes the report. (CL)