Accumulating evidence links brown adipose tissue(BAT) to increased cold-induced thermogenesis (CIT) and the regula-tion of lipid metabolism in humans. BAT has also been proposed as anovel source for biologically active lipid mediators including polyun-saturated fatty acids (PUFAs) and oxylipins. However, very little isknown about cold-mediated differences in energy expenditure andvarious lipid species between individuals with detectable BAT(BATpos) and those without (BATneg).