Three revolutions in the history of mental health were identified by Nicholas Hobbs: the humane revolution, the scientific and therapeutic revolution, and the public health revolution. The shift of responsibilities for mental health and substance abuse services from the public to the private sector may constitute a fourth mental health revolution. The public-private issue can be viewed from two historical vantage points: developments in American medicine and specific developments within mental health. The reprivatization of medical care in America involves a change in type of ownership and control; horizontal integration; diversification and corporate restructuring; vertical integration; and industry concentration. In the field of mental health, recent developments have been toward reprivatization and deinstitutionalization. There are differing views on what values will be emphasized as a result of the reprivatization of mental health, but the reassessment of public and private responsibility should be pursued within the context of history. The sense of realism and caution that history demands should prevail as the public interest in mental health is sought. (NB)