One group of 10 obese people (1.72 times normal weight) was compared to a control group of 9 normal-weight subjects. Oxygen consumption (VO2), immuno reactive growth hormone (IRGH), and rectal temperature (Tre) were measured every 15 min on an average, during the 5 h following a protein meal composed of 6 egg-whites and 50 g of casein totaling 1 340 kJ. The results show that postprandial thermogenesis (PPT) is the same in both groups: maximum increase in VO2 averages 15% in the obese and 16% in the control groups respectively. Energy expenditure integrated over the 5 h was 129 kJ for the obese and 114 kJ for the control subjects, i.e. 9.6% and 8.5% of the energy meal content. The rise in Tre was identical for both groups (0.4 degrees C over 3 h). For IRGH, the preprandial reference figures were much lower in the obese: 52 pmole.dm-3, as compared to 145 pmole.dm-3. In all control subjects, the protein meal resulted in a IRGH peak of, on average, 455 pmole.dm-3 about 2 h after. This was not observed in 4 of the obese subjects, while in the remaining 6, the mean peak value was 165 pmole.dm-3, occurring after 1 h. The other hormonal or chemical compound simultaneously analysed (glucagon, cortisol, PRL, T3, glucose, lactate, NEFA) do not show any significant variations but insulin blood level for which a postprandial increase was measured in both groups. It is concluded that after a protein test meal: PPT in overweight people is no different from that in people of normal weight.(ABSTRACT TRUNCATED AT 250 WORDS)