Meta-analysis was used to examine 108 intervention comparisons in 39 controlled smoking cessation trials. Type of intervention (face-to-face advice being better than all others), type of intervenor (both physician and nonphysician counselors better than either alone), the number of reinforcing sessions, and the duration of reinforcing sessions were related to success six months after the initiation of intervention. The number of modalities used by the intervention predicted success with borderline statistical significance. Multivariate analysis predicted that a team of physicians and nonphysicians using multiple intervention modalities to deliver individualized advice on multiple occasions would produce the best result. Program success 12 months after the initiation of intervention was related to the type of intervention session (group and individual sessions combined better than either alone), the number of intervention modalities, and the number of reinforcing sessions. With multivariate adjustment for confounding, the number of intervention modalities alone had a positive association with intervention success.