The thermomodel 2C4T to assess oxygen consumption and a flow through method (FM) were synchroneously applied to 16 neonates in order to determine the validity of the thermomodel (TM). The newborn infants were healthy, had a gestational age (mean±SD) of 33.1±3.3 wks, a postnatal age of 20±18 days and a weight of 1.97±0.5 kg at the time of study. All newborns were nursed in an isolette single wall incubator with an operative environmental temperature of 30.5±1.1°C and a relative humidity above 70%. They were studied being naked and lying supine for a period of 60 min before and 40 min after feeding. For the flow through method we used a gas flow of 1 to 2 1/min.kg bodyweight sucked through a plexiglas hood, measured by pneumotachography and calibrated by a spirometer; and an oxygen analyzer OM11 (Beckman) the input of which received dry gas at stable pressure and temperature. The oxygen consumption (VO2) was calculated as product of flow and oxygen concentration difference. The thermomodel was applied the standard way. The mean VO2 during the study period was 7.00ml/kg.min determined by the FM and 7.97ml/kg.min by the TM. The VO2 correlated statistically significant with the VO2 (r=0.58, N=188, y=3.21+0.68x,p<0.0001). The difference between VO2TM and VO2FM in each pair of measurement averaged 0.97ml/kg.min with a standard deviation of 1.44 ml/kg.min. All original data will be presented to demonstrate the good intra-individual correlation between VO2TM and VO2FM. The thermomodel reliable reflects relative VO2 changes but requires improvement to measure absolute V02 with greater accuracy.