Presents evidence for the validity of the Contemplation Ladder, a measure of readiness to consider smoking cessation. Analyses of data collected from more than 400 smokers at two worksites before and during a 10-month intervention indicate that Ladder scores were significantly associated with reported intention to quit, number of previous quit attempts, perceived co-worker encouragement to quit, and socioeconomic status. Ladder scores predicted subsequent participation in programs designed to educate workers about their smoking habit and its contingent risks. The Ladder did not predict biochemically validated abstinence of 24 hr or more. To assess its ability to distinguish between groups known a priori to differ in readiness, we administered the Ladder to 36 participants in a clinic-based smoking cessation program. As predicted, clinic patients scored significantly higher than the workers on the Ladder. The importance of distinguishing between smokers at the lowest stages of readiness to quit is discussed.