In 76 smokers, correlations between plasma nicotine and alveolar carbon monoxide levels of the individual smoker and the nicotine and CO yields of his cigarette were very poor. In 24 smokers of low-nicotine, low-tar cigarettes, mean alveolar CO levels did not differ from those of smokers of regular cigarettes. Mean plasma nicotine levels were lower in smokers of low-nicotine cigarettes, but a wide overlap of individual values occurred. The implication that an individual shifting to ultra-low-tar cigarettes reduces risks of cardiopulmonary disease is unwarranted.