RJRT has explored two approaches for determining nicotine uptake from use of smokeless tobacco products (STPs) and cigarettes in smokers. In a “dual use” design, subjects smoked ad libitum until 30 minutes before in-clinic assessment. Subject assessment involved use of a tobacco product and periodic blood collections before, during, and after product use for measurement of serum nicotine concentrations. For some STPs, serum nicotine concentrations decreased during use, indicating that the elimination rate of pre-existing nicotine from same-day smoking was greater than uptake from the STP. Therefore, estimation of nicotine uptake from STPs required adjustment for baseline nicotine from same-day smoking. To do so, we assumed nicotine decayed following first-order kinetics and used a published nicotine half-life of 120 minutes. Baseline nicotine remaining at each time point was calculated and subtracted from the observed concentrations. Area-under-the-curve (AUC) was calculated using the adjusted concentrations. In the abstinence design, smokers abstained from all nicotine-containing products, including cigarette smoking, for 12 hours prior to in-clinic assessment. The longer nicotine abstention minimized baseline nicotine levels, resulting in a smaller impact of nicotine decay than in the dual-use design. The previously described adjustment for incoming nicotine was performed, and baseline-adjusted AUCs were calculated. Results from the two study designs were in good agreement for all STPs evaluated. Cigarette AUC results from some dual use studies were lower than the corresponding AUC results from the abstinence design. Average baseline-adjusted AUCs for products ranked as follows: Cigarettes > Camel Snus > Camel Stick > Camel Strip. The dual use design, with same-day smoking and minimal 30-minute abstinence, provided valid and accurate estimates of nicotine uptake in spite of generally larger variability.