We review the various ways in which telephone counseling has been used in smoking cessation programs. Reactive approaches--help lines or crisis lines--attract only a small percentage of eligible smokers but are sensitive to promotional campaigns. While difficult to evaluate, they appear to be efficacious and useful as a public intervention for large populations. Proactive phone counseling has been used in a variety of ways. In 13 randomized trials, most showed significant short-term (3-6 month) effects, and four found substantial long-term differences between intervention and control conditions. A meta-analysis of proactive studies using a best-evidence synthesis confirmed a significant increase in cessation rates compared with control conditions [pooled odds ratios of 1.34 (1.19-1.51) and 1.20 (1.06-1.37) at short- and long-term follow-up, respectively]. Proactive phone counseling appeared most effective when used as the sole intervention modality or when augmenting programs initiated in hospital settings. Suggestions for further research and utilization are offered.