Smokers generally have lower body weights than non-smokes and tend to gain weight after smoking cessation. The weight gain that occurs when smokers quit is a major reason many smokers give for not abstaining and is a significant cause of smoking relapse following cessation. This proposal is designed to investigate which aspects of the energy balance equation--caloric intake or expenditure--are involved in nicotine's effects on body weight. The focus will involve both the chronic effects of smoking status and the acute effects of nicotine on caloric intake, including perceived appetite, caloric consumption, satiety, and taste sensitivity and preference, and on caloric expenditure, including leisure time activity and fatigue, resting metabolic rate (RMR), and diet- and activity-induced thermogenesis (DIT, AIT). Study I will examine differences between 20 smokers and 20 non-smokers in reported daily food intake, ratings of sensitivity and preference for graded samples of sweet, salty, sour and bitter food, caloric consumption during a standard meal, and appetite and satiety ratings before and after the meal. This study will also investigate nicotine's effects on appetite and taste sensitivity and peference ratings by comparing smokers' ratings before and after receiving 1 mg. nicotine via inhalation with those before and after receiving placebo. Study II will examine the dose-response and cumulative effects of nicotine on RMR by presenting during 3 separate sessions 0 mg. (placebo), 1 mg., or 2 mg. nicotine every 30 minutes for 2 1/2 hours (5 presentations) to each of 20 smokers. Study III will investigate differences between 80 smokers and 40 non-smokers in RMR and DIT by presenting a caloric load or water, and will examine the acute effects of nicotine on RMR and DIT in smokers by administering nicotine or placebo following the caloric load or water. Nicotine's effect on DIT may relate to the efficiency of caloric storage in smokers. Finally, Study IV will investigate differences between 80 smokers and 40 non-smokers in reported leisure time activity and in AIT, and will examine in smokers the acute effects of nicotine on AIT and fatigue during a lighit workload. Nicotine's effect on AIT may indicate whether the caloric expenditure of daily activities is increased when performed while smoking. The results of these studies may offer directions for future research in the development of adjunct treatment for smoking cessation to prevent weight gain and thus reduce the likelihood of smoking relapse.