In recent years, mutual help groups have been formed to address problems in substance abuse, chronic physical illness, mental illness, marital disruption, and child abuse. Despite the proliferation of these groups, little research has been conducted to assess their efficacy or what happens in them. The nature of mutual help groups (N=32) was investigated by comparing them to psychotherapy groups (N=35), social-recreational groups (N=59), and task-oriented groups (N=39) on 10 social climate dimensions derived from the 90-item Group Environment Scale. The 10 dimensions were cohesion, leader support, expressiveness, independence, task orientation, self-discovery, anger and aggression, order and organization, leader control, and innovation. The results revealed that all 10 dimensions yielded significant differences. Compared to psychotherapy groups, the mutual help groups had a more active leadership role and greater group cohesion in addition to being more structured and task-oriented and fostering more independence. The psychotherapy groups were more encouraging in the expression of negative and other feelings and showed more flexibility in changing the groups' functions and activities. Future research should assess outcomes in various domains in the different groups to determine the ultimate impact of social climate characteristics on people's adjustment and well-being. (Author/NRB)