BACKGROUND: Nonsmokers have a potentially supportive role in tobacco cessation efforts. The present study examined the feasibility, acceptability, and potential efficacy of a telephone-based intervention for nonsmoking support persons. METHODS: A total of 59 support persons (mean age = 36 years, 92% female, 95% White) were randomly assigned to a control condition (N = 30; written materials only) or to a social cognitive theory-based intervention (N = 29; written materials and 5 weekly, 20- to 30-min telephone counseling sessions). Both support persons and smokers completed assessments separately by mail at baseline and at weeks 6 (end of treatment) and 26. RESULTS: Two thirds of the smokers reported low-moderate levels of motivation to quit at baseline as assessed by the contemplation ladder. Study retention rates were excellent, with 95% of both support persons and smokers completing the week 26 assessment. Moreover, 86% of support persons in the intervention group completed all five telephone sessions. Treatment acceptability was high for both support persons and smokers. Compared with the control condition, the intervention was associated with a significant increase in support person self-efficacy to help their smoker (p = .034) and outcome expectancies (p = .025) from baseline to week 6. However, the intervention was not associated with higher smoking abstinence rates or quit attempts. DISCUSSION: The program was successful in reaching smokers with lower levels of readiness to quit. The intervention was feasible and acceptable to both support persons and smokers. Although support persons and smokers can be engaged in this type of outreach program, refinements in the intervention approach are needed to improve the smoking outcomes.