Abstract
Measurements of nicotine and cotinine in human body fluids have become accepted as means of assessing nicotine uptake and inferring smoke uptake. In two long-term studies of human smoking behaviour the usefulness and reliability of body fluid measurements is questioned. An alternative approach for measuring nicotine uptake is suggested and investigated where the retention of nicotine is measured, thus eliminating variability due to inter-individual differences in nicotine metabolism and subsequent errors due to timing of sampling. This method is used to investigate the paradox that exists in cigarette smoking where effects occur which are more rapid in onset than was thought possible due to the absorption of nicotine from the particulate phase of cigarette smoke with which nicotine is associated. From the experimental evidence and associated discussion a three-phase mechanism for uptake of nicotine during the smoking process is proposed.