WITH THE rediscovery of the environment in the treatment of the mentally ill, terms such astherapeutic milieu, therapeutic environment, andtherapeutic communityhave become commonplace, in spite of imperfect agreement regarding their definitions or effects. Among the diverse and sometimes vague meanings that have been used are: a pleasant background for treatment, a type of comprehensive treatment program, something in between these, humanizing the hospital, the ethos or emotional climate, attitudes or ideology of the staff, qualities of relationships, types of organization, and physical settings.1One of the reasons for an inability to predict the effects of specific aspects of the treatment environment on particular types of patients2,3is that research in this area suffers from inadequate conceptualization and measurement of environmental differences. The development of an instrument to measure the "Characteristics of a Treatment