Measured resting energy expenditure (REE) was compared to predicted basal energy expenditure (BEE) in 35 consecutive patients with nonseptic inflammatory bowel disease (IBD) and 20 healthy volunteers. Patients with IBD were groups greater or less than 90% ideal body weight (IBW). The BEE in kcal/day was found to be equivalent to the measured REE in both patient groups. It is suggested that the BEE be used to determine caloric requirements in nonseptic patients with inflammatory bowel disease. Patients less than 90% IBW had significantly higher measured energy expenditure (26.4 +/- 1.0) per kg body weight than either controls (21.2 +/- 0.7) or patients greater than or equal to 90% IBW (21.2 +/- 0.8), p less than 0.001. It is suggested that this increased expenditure is due to a combined effect of weight loss and intrinsic disease.