The effects of nicotine-containing chewing gum on cigarette smoking and subjective and physiological response were evaluated in eight normal volunteers. Isolated subjects smoked their regular brand of cigarettes freely in a naturalistic laboratory environment while watching television or reading. Before 90-min smoking sessions subjects chewed two pieces of placebo or nicotine-containing gum (0, 2, 4, or 8 mg) under double-blind conditions. Each subject received each treatment four times in a mixed order across days. Analysis of the chewed gum for remaining nicotine revealed that the mean delivered nicotine doses were 0, 1.02, 2.39, and 5.20 mg nicotine. Nicotine preloading produced dose-related increases in plasma nicotine, while producing dose-related decreases in various measures of cigarette smoking including number of cigarettes smoked, number of puffs taken, expired air carbon monoxide level, and ratings of smoking satisfaction. Nicotine preloading produced dose-related increases in ratings of gum dose-strength, while producing decreases in ratings of gum dose acceptability and liking. Heart rate and blood pressure were not significantly affected by nicotine gum. Taken together, the present results confirm that responses to nicotine in the gum preparation are orderly and related to dose, and the results suggest that the efficacy of treating tobacco dependence with nicotine gum may be enhanced by increasing the administered dose.