Energy metabolism was measured at the bedside in 22 uncomplicated surgical patients in the early (24 to 48 h) postoperative period with the use of continuous computerized indirect calorimetry with a canopy system. Energy production rates were higher than those predicted by the Harris-Benedict formula both in absolute value (1516 ± 61 vs. 1387 ± 49 kcal/day,p< .05) and when normalized by body weight (BW; 23.5 ± 0.5 vs. 21.7 ± 0.5 kcal/day kg BW,p< .01) or by lean body mass (LBM; 32.8 ± 0.8 vs. 30.2 ± 0.9 kcal/day kg LBM,p< .01). Furthermore, surgical patients had higher energy production rates than those measured in 22 overnight fasted, resting healthy subjects matched for age, sex, and body size (23.5 ± 0.5 vs. 21.8 ± 0.6 kcal/day · kg BW,p< .05). In both the patients and the control group, measured energy production bore a direct relation to LBM.We conclude that the early postoperative period of uncomplicated surgery is associated with a small (about 7%) but consistent increase in energy metabolism above the level observed in the overnight fasted, resting healthy individual. This increase appears to be an effect of surgery itself, and is not predicted by Harris-Benedict equations.