We have recently conducted a detailed study of smoking behaviour in young people, recording and measuring the number of cigarettes smoked, the number and duration of puffs taken, and the volume of smoke inhaled per puff/cigarette. We would now like to identify molecular markers of smoking behaviour in saliva. Although saliva cotinine levels accurately indicate recent nicotine intake, it does not capture long-term exposure or different smoking behaviours that are likely to impact on disease risk. DNA methylation is known to be an extremely stable and sensitive marker of smoking status that is predictive of smoking-related disease risk. It has also been used with some success to detect prenatal smoke exposure, own smoking pack-years and time since cessation. Several of our study participants are ALSPAC participants who recently provided saliva samples in the most recent ALSPAC clinic. We would like to use these samples to generate DNA methylation profiles in order to examine the extent to which detailed smoking behaviours are reflected in DNA methylation patterns.