Pretest and posttest scores on the Edwards and the Marlpwe-Crowne Social Desirability scales and the 12 scales of the Personal Orientation Inventory were administered 4 days before and 4 days after participation in a 15hour marathon group experience. Scores in this experimental condition were compared with pretest and posttest scores in a control condition in which subjects received the same tests without the intervening group experience. Participants in the marathon group demonstrated a significant decrease in defensiveness and constriction and showed change in the direction of more socially positive functioning on 13 of the 14 scales employed. A nonsignificant tendency was found for control subjects to show improvement on many of these scales also.