Increased resting energy expenditure has been postulated to be one of the contributory factors in the development of cancer cachexia. Body composition and resting energy expenditure were evaluated in six male and seven female normal controls in order to validate methodology. Identical methods were then applied to seven male sarcoma patients with localized disease. Only the age and sex-matched group of controls were compared to the sarcoma patient group. All patients had received no prior cancer treatment. Body composition assessment included measurement of body fat using four-site skinfold measures. measurement of total body potassium (40K) as an indicator of body cell mass. and calculation of body surface area. Resting energy expenditure was measured by indirect calorimetry in an enclosed plexiglass hood and compared to predicted resting energy expenditure as determined by the Harris and Benedict formulae. Measured resting energy expenditure per unit body surface area was significantly increased in the sarcoma group: 1610.7 +/- 369.2 (sarcoma) vs. 1290.3 +/- 74.3 kcal/m²/day (controls), p<.05. Percent body cell mass was significantly decreased in the sarcoma group: 32.6 +/- 3.8% (sarcoma) vs. 39.8 +/- 3.7% (controls), p<.05. Predicted resting energy expenditure underestimated measured values by 42.1 +/-13.0% in the sarcoma group and 29.7 +/- 5.4% in the control group. Results of this study suggest that in otherwise asymptomatic cancer patients with metabolically active tumors, such as sarcomas, increased resting energy expenditure contributes to the onset of cancer cachexia prior to any signs of overt host depletion. / M.S.