Five male smokers were tested, after 48-h abstention from tobacco-product use, smoking a leading "lights" category cigarette (Control-FTC nicotine yield 0.6 mg) and another cigarette yielding similar amounts of "tar" and carbon monoxide (CO), but only 0.06 mg nicotine (Test). Heart rate (HR) and the electroencephalogram (EEG) were monitored before, during and after the smoking of each cigarette. Other measures obtained included the subjects' puffing and breathing behaviors during smoking, plasma nicotine concentrations, blood carboxyhemoglobin concentrations and expired-air CO. The results indicated no significant differences in the way the subjects puffed and inhaled the two cigarettes and they were therefore assumed to have inhaled similar amounts of particulate matter and gas-phase components. Plasma nicotine concentrations were significantly higher following smoking of the Control cigarette. HR (percent relative change) increased following smoking of either cigarette; however, HR increase was significantly greater following smoking of the Control cigarette. Smoking the Test cigarette had no effect on the EEG. Smoking the Control cigarette produced a significant increase in beta 2 magnitude and a significant decrease in delta magnitude. This indicates that the effects of smoking on the EEG are a function of nicotine absorbed from cigarette smoke upon inhalation and not a function of inhaled particulate matter, CO, or other gas-phase components.