Maintenance of health behavior change over the long-term has been routinely difficult. One of the reasons for this difficulty is that only individuals' attitudes or behavior are changed, without concomitant support from the social environment. The purpose of this study was to explore several of the ways in which significant others--family members, friends, and coworkers--may affect changes in health behavior. Eighty-four participants in a work site health promotion program were the subjects of the study. Self-reports of health behaviors were gathered at baseline and at the end of the 7-week program; in addition, subjects reported the extent to which significant others generally supported health behavior changes, encouraged them to maintain changes they had made, and made changes in their own health behaviors. Results provide support for the general hypothesis that one individual attempting to change health behavior may be positively influenced by significant others during the course of the change process. Family members were particularly helpful, and overall supportiveness was more helpful than others' change in health habits or encouragement. Behaviors most influenced by others were exercise and fat consumption. Suggestions for future theoretical development, research, and intervention are discussed.