Harm reduction for tobacco smokers may involve reducing their exposure to lethal smoke constituents. Assessing smoke constituent exposure and any resulting harm reduction from a potential reduced-exposure product (PREP) will involve preclinical, clinical, and epidemiological research. The purpose of this study was to evaluate a clinical laboratory model for assessing the acute effects of PREPs for smokers. Philip Morris' Accord and R.J. Reynolds' Eclipse were used as examples. Twenty overnight-abstinent smokers (> 15 'light' or 'ultra-light' cigarettes/day) participated in 4 Latin-square ordered, 2.5-hr sessions in which they completed an 8-puff smoking bout every 30 minutes. Sessions were separated by at least 24 hours and differed by product used: own brand, denicotinized tobacco cigarettes, Accord, or Eclipse. Tobacco withdrawal and carbon monoxide (CO) were assessed before and after smoking, heart rate was assessed before and during smoking, and puff volume, duration, and interpuff interval were assessed while subjects smoked. Blood was sampled at the beginning and end of each session. Relative to normal cigarettes, Accord was less effective at suppressing withdrawal and produced minimal CO boost despite the fact that, when using Accord, subjects took bigger and longer puffs. Eclipse suppressed withdrawal fully and increased CO boost by approximately 30%. Own brand, Accord, and Eclipse, but not denicotinized cigarettes, increased plasma nicotine concentration. Taken together, these results suggest that neither Accord nor Eclipse is likely to be an effective reduced-exposure product for smokers and that this clinical laboratory model is valuable.