Energy expenditure (EE) was measured, during 3 consecutive days, in six patients suffering from acute pancreatitis. Measurements were achieved postoperatively, under mechanical ventilation, using a mass spectrometer system. EE represented 1.49 times (range: 1.08-1.78) the predicted resting energy expenditure (PREE) according to the reevaluated Harris-Benedict equation. There was a weak positive correlation between EE and core temperature and a negative correlation between EE and nitrogen balance. EE/PREE was not different between septic and nonseptic patients (1.58 +/- 0.06 vs. 1.39 +/- 0.07). The calculations of nutrient oxidation rate indicated a high protein catabolic rate, a neoglucogenesis, and a lipolysis.