Worksite competitions have shown promise in facilitating smoking cessation among employees, but the effectiveness of the competition component itself has not been determined. A multicomponent behavioral treatment and maintenance program plus nicotine gum were provided to competition and no-competition conditions at two large worksites. At 1-year follow-up, 100% of subjects were contacted and measurement of expired carbon monoxide validated abstinence. Recruitment rates were significantly higher in the competition group (2% of smokers) than the no-competition group (0.6% of smokers, P less than 0.001). One-year abstinence rates were 50% for the competition group and 25% for the no-competition group. This difference was not statistically significant (P less than 0.25). However, survival analysis revealed a significant difference in number of weeks abstinent during the year after treatment. Mean weeks abstinent was 35 for competition and 22 for no-competition (P less than 0.05). At the 3-month follow-up, the number of boxes of nicotine gum used predicted abstinence (P less than 0.002). At the 1-year follow-up, rated supportiveness of one's "buddy" (P less than 0.01) and number of sick days prior to starting the program predicted abstinence (P less than 0.003). It is suggested that competition, nicotine gum, and social support may enhance worksite smoking cessation program rates.