Previous studies have demonstrated reductions in exposure to selected smoke constituents in smokers who switch from conventional cigarettes (CC) to an electrically heated cigarette smoking system (K6) under controlled smoking conditions. The aim of this study was to make a preliminary investigation of changes in a variety of candidate biomarkers of effect (BoEff) and exposure (BoExp) in subjects after smoking K6 cigarettes for one month under real-life conditions. This clinical investigation was a single-centre, randomised, open-label, two-arm study. Caucasian smokers aged from 30 to 60 years were enrolled and randomised to one of two groups: those who would continue to smoke conventional cigarettes (CC) and those who would switch to smoking the K6 cigarette for one month. A selection of BoExp and BoEff in blood and urine were compared between study groups at study end. This study was conducted in Poland from October 2007 to April 2008 in accordance with the principles of good clinical practice. A total of 338 subjects were enrolled, of which 316 were randomised to either the CC study arm (n=79) or to the K6 study arm (n=237). A number of BoExp for smoke constituents were measured in this study.