Eighteen encounter groups were studied, representing lo approaches to personal change: T Groups, Rogerian, personal growth, sensory awareness, Gestalt, transactional analysis, psychodrama, Synanon, marathons, psychoanalytic, and Berzon's PEER Tapes. The study aims were (a) to assess the impact of such experiences for participants and (b) to isolate the group conditions associated with change. College undergraduates who expressed interest in having an encounter group experience were randomly assigned to the groups. A control group of 69 persons supplied data for contrast with those collected from the 209 experimental participants. Outcome assessment procedures were developed to assess (i) peak experiences, (2) self-esteem and self-ideal discrepancies, (3) values, (4) life decision making, (5) interpersonal orientation, (6) interpersonal constructs, (7) coping styles, and (8) interpersonal ftyles. Individuals were tested prior to group assignment, at the end of the three-month experience (30 hours of group), and again six/eight months later. Other sources of outcome data included (a) leader ratings, (b) peer group ratings of in-group behavior, and (c) external 'social network" judgments of change. All group sessions were attended by systematically rotated observers, who made codings of Content, working pattern, emotional climate, themes, normative behavior, rewarding and sanctioning behavior, and leader behavior and style. Other measures of group conditions were derived from participants, including questionnaircs on norms, cohesion, member roles, and Ss' phenomenal view of critical group events and major learning experiences. Preliminary findings are reviewed, including evidence on both positive and negative outcomes, and the relationship of leader behavior to each.