This randomized, open-label, ambulatory, controlled clinical study investigated biomarkers associated with cardiovascular risk and biomarkers of exposure to 10 selected harmful and potentially harmful constituents (HPHC) in cigarette smoke in 316 male and female Polish smokers. Subjects were randomized to continue smoking conventional cigarettes (CC; N=79) or switch to smoking the Electrically Heated Cigarette Smoking System series-K cigarette (EHCSS-K6; N=237). Biomarker assessments were performed at several time points during the study at baseline and during the 1-month investigational period. The primary biomarkers were high-sensitivity C-reactive protein and white blood cell counts. No statistically significant differences in the two primary biomarkers were found between the study groups at the end of the study. End-of-study comparisons of secondary biomarkers between study groups indicated an increase in high-density lipoprotein cholesterol, and reductions in red blood cell count, hemoglobin, and hematocrit levels in the EHCSS-K6 group. All biomarkers of exposure to cigarette smoke HPHC were decreased in the EHCSS-K6 group, despite an increase in cigarette consumption, compared to the CC group. There were no apparent differences in any of the safety assessment parameters between the groups, and the overall incidence of study-related adverse events was low.