Successful rehabilitation of the chronic mentally ill quite often depends on interventions in the social environment (Shepherd 1989). Enhancement of social functioning means optimalizing existing social roles and facilitating a productive environment in which the patient can explore new roles (Bennett 1978). For the judgement of social functioning some seven instruments have been translated into the Dutch language (the SBAS, the DAS, the SIS, the SAS, the GSB, the NOSIE and the IPPO; footnote). Most of these instruments were made for research purposes. None of them gives any information about lifetime development in social functioning. In the chronic mentally ill behaviour is a result of longterm interaction with the direct personal environment (Adler 1984). This article shows how the development of social functioning can be analized. The principles of an instrument to be used as a starting point for intervention are illustrated with a case-history. The instrument is developed in a collaborative study of the Department of Social Psychiatry, University of Limburg, and the Service for chronic mentally ill of the Community Mental Health Centre, Maastricht, Holland.