This study employed structural equation modeling techniques to examine hardiness and self-efficacy as potential mediating personal variables in the relationship between social support and exercise behavior. 282 females (aged 20-86 yrs) participated in a 5-wk aerobic fitness program. During the 2nd wk of the exercise program, Ss completed a questionnaire consisting of the Social Provisions Scale, the Exercise Self-Efficacy Scale, a hardiness scale, and demographic datAt the conclusion of the 5th wk, Ss completed a short questionnaire assessing their perceptions of success and self-efficacy related to continued involvement. Findings indicate that hardiness served a mediational role in the relationship between social support and self-efficacy. Efficacy cognitions, in turn, were directly related to exercise behavior. In support of this model, no direct relationship between social support and exercise behavior was found. Findings indicate that social support may lead to increased levels of internal control, commitment, and confidence. These results suggest that social support, hardiness, and self-efficacy are related psychosocial variables that, in some populations involved in exercise, function from within the same theoretical framework.