The aim of the study was to measure the changes in energy expenditure (EE) and respiratory quotient (RQ) induced by fever in children receiving total parenteral nutrition (TPN). Ten children aged 1-16 years (weight for height: 104.5 +/- 13%) were included. They underwent two EE recordings of 3 h duration using indirect calorimetry, during a febrile (38.9 +/- 0.5 degrees C) and afebrile conditions, after parameters (nutritional intake, ambient temperature) being equal. The EE, (febrile phase) was significantly higher than the EE(2) (afebrile) (2.13 +/- 0.48 vs 1.78 +/- 0.42 kcal/kg/h; P < 0.01). Increase in EE was significantly correlated with body temperature (r = 0.92, P < 0.001). The slope of the regression line indicates an increase of 16.2% in EE per degree of fever. By dividing the individual increase in EE by the individual increase in temperature, the energy expenditure during fever is 11.3% per unit rise ( degrees C). During the febrile phase urinary nitrogen excretion was significantly higher (280 +/- 90 vs 210 +/- 70 mg/kg fat free mass/day, P < 0.02). The RQ during the febrile phase (0.90 +/- 0.13) did not differ significantly from mean RQ during the afebrile phase (0.95 +/- 0.07). Fever due to infection or inflammatory process is partly responsible for an hypermetabolic state including increased EE.