Rats infused with nicotine were initially hypophagic and lost weight. Although food intake recovered, body weight remained 8-12% below normal. Elevating (or reducing) body weight before treatment prolonged (or shortened) initial hypophagia; weight reliably stabilized at the reduced level. At this reduced weight, the treated rats' daily resting energy expenditure was comparable with that of normal-weight controls (262.3 vs 261.9 kJ.d-1.kg body wt-0.75). Reducing the weight of controls to that of treated rats caused their expenditure to drop to 250.6 kJ.d-1.kg body wt-0.75, an energy-conserving adjustment that treated rats also displayed when their weight was lowered from its already-reduced level. Terminating nicotine treatment led initially to hyperphagia, which abated upon body weight being restored to normal. Normal daily energy expenditures at reduced weights suggest that nicotine lowers regulated body energy. Acute intake adjustments associated with initiation (or cessation) of nicotine treatment can be viewed as responses appropriate to bringing body energy into balance with the altered regulation level.