Human smoking behavior is characterized by a wide spectrum of smoking patterns which result in significant variations in "tar" and nicotine exposure. In an ongoing, large population study we are measuring puff volume, duration, interval between puffs and number of puffs taken, as well as cigarette butt length, for smokers of low- and medium-nicotine cigarettes using a microcomputer-assisted flow transducer. The study has a multi-factorial design aimed at evaluating differences in smoking behavior and exposure to cigarette smoke constituents between White American and African-American smokers of both genders. On average, smokers of low- and medium-nicotine cigarettes both draw 48 mL puffs every 23 seconds, yielding a total volume per cigarette of 610 mL. More than 80% of the smokers puffed more intensely than machines operated with the CORESTA/FTC parameters ( i.e ., they drew puffs larger than 35 mL and left intervals between puffs of less than 30 seconds instead of 58 sec.). The average smoke yields per cigarette as determined by simulating human smoking behavior were 2.3 mg nicotine and 27 mg "tar". Moreover, we found that the differences in the administered doses of smoke constituents are not driven as much by the type of cigarette but by overall smoking patterns and number of cigarettes smoked per day. A comprehensive statistical analysis of smoking patterns and actually inhaled doses of specific smoke constituents will be presented in detail. The implications of our findings will be discussed.