We studied the hemodynamic effects of smoking cigarettes with high and low contents of nicotine in young smokers free of coronary arterial disease. The smoking of one cigarette with a high content of nicotine produced a peak rise in cardiac output of 32 percent above baseline values, and the effect persisted for one hour. Smoking a cigarette with a low content of nicotine produced a peak rise of 13 percent above baseline values, with a duration of five minutes. The rise in cardiac output was almost entirely attributable to tachycardia, since stroke volume remained relatively constant. The smoking of a cigarette with high nicotine content also caused greater and more sustained elevation in systemic blood pressure than smoking a cigarette with low nicotine content. Thus, there was a responsiveness to the dose of nicotine in cigarettes smoked by young smokers free of coronary arterial disease.