Nicotine polacrilex ("nicotine gum") is effective in helping persons to quit smoking cigarettes. Because many persons try to quit without formal assistance, it may be an appropriate product for over-the-counter (OTC) purchase. Some smokers, however, might use such a product in lieu of more effective methods of cessation, and still others might use it to cope with enforced periods of nicotine abstinence (eg, at the work place) and thereby delay their decision to quit. The study's objective was to assess the public health benefits and risks of OTC availability of nicotine gum. A Markov model was developed and used to contrast two alternative policy scenarios: one in which nicotine gum was assumed to remain available only by prescription, and another in which it was assumed to be made available for OTC purchase. Various data sources were used to estimate the model, including the Health Promotion and Disease Prevention Supplement to the 1991 National Health Interview Survey and the 1986 Adult Use of Tobacco Survey. Primary outcome measures included the numbers of persons who would try to quit smoking, the numbers who would use various methods of smoking cessation, including OTC nicotine gum, and the numbers of current adult smokers who would be abstinent at the end of 10 years. Findings suggest that an average of 3 million persons each year would use OTC nicotine gum. As a consequence of OTC availability, an additional 450,000 smokers would be abstinent at the end of 10 years. These results are sensitive to assumptions regarding the effectiveness of OTC nicotine gum, as well as to the effect of OTC availability on the use of other methods of smoking cessation. The number of persons who would quit smoking, however, increases under a fairly wide range of assumptions. Over-the-counter availability of nicotine gum may confer significant public health benefits.