The incremental effects of competition and relapse prevention training were evaluated in the context of a multicomponent worksite smoking modification program. Subjects were 136 adult smokers (72 men; 64 women) recruited from eight worksites in Fargo, ND (n = 4) and Eugene, OR (n = 4) in a two (competition/no competition) by two (relapse prevention training/no relapse prevention training) design. Ninety-three percent (127/136) of subjects completed the program and 96% of these participants (122/127) completed the 6-month follow-up. At post-test, subjects in the competition conditions achieved a higher cessation rate (39%) than participants in the no competition conditions (16%; x2 = 8.26, P < 0.004). At follow-up, there were no longer significant differences in cessation rates among conditions, although non-abstinent subjects in the competition condition had significantly lower carbon monoxide levels than non-abstinent subjects in the no competition condition. No effects for the relapse prevention manipulation were observed. It is concluded that competition and incentive-based programs can achieve impressive reductions in smoking. Suggestions for reducing long-term relapse and directions for future worksite smoking modification research are offered.