Purpose. To assess organizational and employee participation during three community wide worksite exercise competitions in two communities. Design. A one-group, posttest-only design was used. Lack of controls, exercise baseline, and the short-term nature of the interventions were limitations. Setting. The Minnesota Heart Health Program conducted annual exercise campaigns between 1982 and 1989 within three intervention communities to reduce behavioral risk for cardiovascular disease. The Shape Up Challenge was a worksite exercise competition designed, in conjunction with other campaign activities, to increase levels of physical activity. Subjects. A total of 19 participating companies in two Minnesota communities and 17,626 employees within these worksites, composed the subjects in this study. Intervention. Eligible worksites were invited to participate in a month-long competition during which employees recorded minutes spent daily in aerobic activities. Incentives were established to promote intragroup cooperation and intergroup competition. Companies competed for awards that were based on average minutes of exercise per employee versus per participant. Measures. Numbers of companies recruited and participating, campaign activities, minutes of exercise, and costs were recorded an implementation logs. Companies completed surveys describing business type, number and sex of employees, existing health promotion programs, and perceived benefits of participation. Results. Of the 365 companies invited to participate, 33% participated (range 15% to 50%). Participating companies were more likely than nonparticipating companies to offer other health promotion programs and perceived greater benefits from participation. Women and smaller companies had significantly greater participation rates than men and larger companies. Average employee participation rates ranged from as high as 84% in smaller organizations to as low as 16% as organization size increased. Conclusions. Community-based worksite exercise competitions appear to be a viable strategy for promoting employee exercise, particularly in smaller companies. Group-based contingencies applied in natural work units may facilitate employee participation. Further research is needed to assess the relative efficacy of this approach, compare alternative incentives, and identify strategies to enhance exercise maintenance after the intervention has ceased.