Measurement of the absorption of cigarette smoke constituents were compared with self-reported daily consumption from 450 smokers to determine the most reliable dose dependent indicator of smoke inhalation and risk for coronary heart disease. A plateau of plasma nicotine and cotinine concentration at levels above 20 cigarettes per day with a continued increase of carboxyhemoglobin and thiocyanate with increasing consumption of cigarettes occurred. Classification of smokers into groups smoking cigarettes yielding more or less than 1 mg nicotine showed that smokers of low yield brands had lower plasma levels of nicotine and cotinine, but comparable levels of carboxyhemoglobin and thiocyanate. Plasma nicotine bore no relationship to smoke inhalation, while the number of cigarettes consumed per day showed a weak correlation to smoke inhalation. Despite the lower nicotine yield of cigarettes, modification in smoking behaviour enabled the smoker to derive as much carbon monoxide and thiocyanate constituents from low and high yield cigarettes; thus counteracting the advantage of low nicotine yield brands. The relationship of these parameters to the risk of coronary heart disease is discussed.