1. The warmest interscapular skin areas were located by thermography in six healthy subjects during ephedrine-induced thermogenesis.
2. In these interscapular areas, and in lumbar control areas, the skin temperature, subcutaneous temperature and adipose tissue blood flow were measured before and during ephedrine-induced thermogenesis.
3. The skin and subcutaneous temperatures increased in the interscapular area as well as in the lumbar area, by about 0.7-1.2°C. The interscapular skin temperature remained about 1°C higher than the lumbar; the subcutaneous temperatures in the two areas were identical during the experiments.
4. Although the interscapular subcutaneous adipose tissue blood flow increased about sixfold and the lumbar increased twofold, the absolute flows were higher in the lumbar area.
5. The oxygen uptake increased to a maximum of 30% above control level.
6. Plasma glucose and glycerol concentrations remained unchanged, and plasma non-esterified fatty acids, lactate and noradrenaline concentrations increased slightly but significantly.
7. Biopsies taken from the hot interscapular areas did not contain brown adipose tissue.
8. It is concluded that the high interscapular skin temperature may be due to a lower insulating fat thickness and that the increases in skin and subcutaneous temperatures during ephedrine-induced thermogenesis are caused by an increased blood flow. These observations weigh against the hypothesis that the interscapular temperature increase is due to functional, interscapular brown adipose tissue.