The influence of cigarette smoking on resting energy expenditure (REE) in normal-weight and obese smokers was investigated. Participants were 20 normal-weight and 20 obese female smokers assessed over a 2-day period. The results indicated that REE increased in both obese and normal-weight smokers after smoking, but the increase was greater for normal-weight participants. The normal-weight group showed a 9.7%, 5.8%, and a 3.6% increase in REE during the three 10-min blocks constituting the 30-min postsmoking phase. However, the obese group showed a 3.9% and a 0.7% increase in REE and a 0.8% decrease in REE during this postsmoking phase. Between-group comparisons revealed a differential rate of change in REE after smoking, indicating that the obese group's change of REE at every postsmoking time point was on average 70 kcal/day below that of the normal-weight group. The metabolic effect of smoking is reproducible, and the obese smokers reliably show an attenuated effect. However, the reliability of the change is lower for both normal-weight and obese smokers. The results have potential implications for discouraging obese persons from taking up smoking and intervening among those who already smoke.