The late arrival of group psychiatry and group psychotherapy has a plausible explanation when we consider the development of modern psychiatry out of somatic medicine. In a particular group a subject may be used as an instrument to diagnose and as a therapeutic agent to treat the other subjects. The doctor as the final source of mental therapeusis has failed. Sociometric methods have demonstrated that therapeutic values are scattered throughout the membership of the group. One patient can treat the other. The role of the healer has changed from the owner and actor of therapy to its assigner and trustee. But as long as the agent of psychotherapy was a particular, special individual, a doctor or a priest, the consequence was that he was also the medium of therapy as well as the catalyzer of healing power.