Although studies indicate a positive association between social support and smoking cessation, clinic-based interventions to increase support for stopping smoking have had limited success. Prior studies have primarily assessed the smokers' perceptions of support received with little attention paid to the support person's reports of support provided. To address this limitation, this study reports on the development and testing of the 22-item Support Interview, a process measure designed to assess supportive behaviors provided to a smoker. The rationale for the conceptual underpinning of the measure and item selection is provided. Preliminary psychometric properties of the instrument (i.e., internal consistency reliability, item-change scores, factor structure) are described. Clinical and public health implications for the use of measures of support provided for behavior change are discussed.