To those smokers who are not able or not willing to quit, Philip Morris International (PMI) is investigating alternative approaches by developing products with the potential to reduce the risks of tobacco-related diseases. These products are now referred to by the US Food and Drug Administration as modified risk tobacco products (MRTPs). The challenge in developing and commercializing MRTPs is two-fold, (i.e., developing tobacco products that are shown to reduce risk and that are acceptable to smokers as substitutes for conventional cigarettes (CC). The Tobacco Heating System (THS) 2.1, the MRTP tested in this study is based on the concept that tobacco is heated at significantly lower temperatures than required for CC. The international Organization on Standardization (ISO) yield per THS Tobacco Sticks were: 7 mg for tar, 0.3 mg for nicotine, and 1 mg for carbon monoxide. There are a variety of nicotine-containing products on the market ranging from cigarettes, oral snuff, chewing tobacco to nicotine replacement therapy products (NRT) (gum, inhaler, nasal spray, etc.). There is a large variability of nicotine absorption across this range of products (Molyneux, 2004). For conventional cigarettes, the nicotine is distilled from burning tobacco and carried on liquid droplets which are inhaled and absorbed rapidly across pulmonary membranes. Blood concentrations of nicotine rise very quickly during a smoking session and peak at the completion of smoking (Henningfield, 1995). It is important to compare nicotine pharmacokinetics for THS 2.1 against CC.