The purpose of this investigation, which has been performed as two studies, was to evaluate the association between the daily exposure to nicotine (measured as cigarette smoking machine yields) and the actual uptake of nicotine by cigarette smokers, as well as the association between oral mucosal changes and the exposure to cigarette smoke. In Study 1, consumption data, soft tissue changes and nicotine intake were measured in 47 habitual smokers using cigarettes with tar and nicotine yields within the ranges 9.3-12.2 and 0.72-1.16 mg per cigarette, respectively. The subjects were divided into three groups based on daily cigarette consumption; group averages (standard deviation) were 10.8 (2.2), 17.9 (1.9) and 28.4 (6.1) cigarettes per day. The group averages of tar deliveries from their usual brands of cigarettes were 11.1, 11.0 and 10.5 mg per cigarette, and group averages of nicotine deliveries were 1.05, 1.05 and 1.06 mg per cigarette, respectively. In Study 2, the same data were measured in a group of 77 habitual smokers with an average individual consumption of 11-21 cigarettes per day. The participants in Study 2 were divided into three groups according to tar delivery from their usual brands to cigarettes, with group averages of tar being 6.4 (1.2), 11.0 (1.2) and 16.0 (1.1) mg per cigarette, and of nicotine being 0.70 (0.12), 1.05 (0.12) and 1.34 (0.08) mg per cigarette, respectively. The average consumption of all three groups was within the range 17.1 to 17.9 cigarettes per day. The daily exposures to nicotine and tar were measured as the smoking machine yields multiplied by the number of cigarettes smoked per day. Nicotine uptake was determined by monitoring nicotine and its seven main metabolites in 24-h urine samples. In Study 1 there were significant differences between the three groups in the total amount of nicotine and metabolites excreted in the 24-h urine. The average nicotine uptake was 14.9, 24.4 and 35.4 mg per day, respectively. In Study 2, the 24-h excretion of nicotine and metabolites was about the same in all three groups and averaged 24.5 mg per day. The nicotine uptake was significantly correlated to the number of cigarettes smoked per day but not to the smoking machine yields of tar and nicotine per cigarette. The average prevalences for each of the different oral mucosal lesions (leukoedema, smoker's palate and hairy tongue) were found to increase with increasing consumption and nicotine uptake (Study 1); they were also independent of tar and nicotine yields from the cigarettes smoked (Study 2). These results indicate that the actual uptake of nicotine by smokers could not be estimated from the smoking machine yields. Reduction in exposure to smoke components may best be accomplished if smokers are encouraged to smoke fewer lower-yield cigarettes and to avoid smoking more of each cigarette.