Health education interventions can be tailored toward stages of change. This strategy is based on theories that predict at which stage which variables are indicative of subsequent behavior change processes. For example, planning is regarded as being effective in intenders. However, rather few studies have tested whether matched interventions are more successful for stage transitions than mismatched ones. Also very few previous studies have identified specific variables as targets of stage-matched interventions. A 2 (condition) x 2 (stages) experimental study tested the effects of stage-matched interventions for 226 participants. The stage-matched intervention moved significantly more individuals forward to action than did the control condition. Stage-specific effects were found to corroborate 78% of the assumptions. Multiple mediator analyses revealed stage-specific mechanisms, indicating that intention and planning facilitated behavior change in intenders. Thus, health behavior interventions should take stages of change into account. (Contains 3 tables and 1 figure.)