This proposal addresses several research priorities related to the regulatory authority of the Food and Drug Administration (FDA) Center for Tobacco Products as mandated by the Family Smoking Prevention and Tobacco Control Act. Scientific evidence supports the important role of tobacco and cigarette smoke carcinogens in the development of cancers associated with cigarette smoking. Regulation of the levels of harmful constituents in cigarette smoke is one of the tobacco control strategies that now can be employed by the FDA and may serve to reduce tobacco carcinogen exposures in those smokers who are unable or unwilling to quit smoking. Such regulation will require a valid and robust approach to the assessment of comparative toxicity and carcinogenicity among various cigarette brands. This proposal will help develop a testing approach that can produce meaningful predictions of changes in human exposure due to changes in constituent levels in cigarette smoke, and hence serve as a reliable measure for product regulation. Thus, the proposed research will generate findings and data that are directly relevant to inform the FDA's regulation of the manufacture, distribution, and marketing of tobacco products to protect public health. The human trial deals with Aims 2 and 3 of this study.

Inclusion Criteria:

• Male or female adult smokers 18-65 years of age, who smoke at least 7 cigarettes per day (to assure that biomarker levels are above the limit of quantitation) and do not have plans to quit smoking in the next month;
• Smoked the same brand for >80% of their cigarettes over the course of at least 1 year, and smoked not more than 20 cigarettes (1 pack) of a different brand within two weeks prior to the eligibility screening;
• Not using any other nicotine or tobacco product;
• Subjects who are not taking any medications that affect relevant metabolic enzymes;
• Women who are not pregnant or nursing;
• Subjects have provided written informed consent to participate in the study (adolescents under the age of 18 will be excluded because this project involves use of tobacco products).

Exclusion Criteria:

• Significant immune system disorders, respiratory diseases, kidney or liver diseases or any other medical disorders that may affect biomarker data;
• Current or recent alcohol or drug abuse problems (to ensure alcohol and drug use does not affect biomarkers of exposure and to maximize retention);
• Regular tobacco use (e.g., greater than weekly) other than cigarettes;
• Currently using nicotine replacement or other tobacco cessation products (to minimize confounding effects of another product);
• Pregnant or breastfeeding (due to toxic effects from tobacco products)
• Report smoking more than 1 pack (20 cigarettes) of a non-usual brand cigarette in the past two weeks * Participants who report smoking 2 or more non-usual brand cigarettes the day before the clinic visit will be ineligible

Adult smokers from Minneapolis-St. Paul metro area