Indirect evidence suggests that smoking low-tar and nicotine cigarettes does not necessarily reduce exposure to these substances. Puff volume, duration and number, interpuff interval, and volume and duration of inhalation were measured while 11 subjects smoked two or four tobacco cigarettes. Nicotine blood levels and breath CO were measured before and after smoking. The machine-determined nicotine yields of the cigarettes correlated (r = 0.52) with the increase in nicotine blood levels after smoking but, when individual differences in smoking behavior were taken into account along with the nicotine yield, there was a stronger correlation with nicotine blood levels (r = 0.84 to 0.93).