A study was made of the comparative effect of cigar and cigarette smoking on the mobilization of free fatty acids (FFA) and the excretion of catecholamines. There was a greater increase in FFA concentration in the serum with cigarette than with cigar smoking. Inhaling during smoking caused a greater FFA response than not inhaling, with both cigars and cigarettes. With tobacco containing glucose randomly labeled with radioactive carbon (14C), there was a greater absorption of14C with cigarette smoking. Urinary catecholamine excretion increased during smoking, significantly more with cigarettes than with cigars. The differences observed with the two forms of smoking probably result from the tendency to inhale with cigarette and not with cigar smoking and from the effect of this on nicotine absorption.