1) The aim of this work was to study the effects of surgical denervation of the interscapular brown adipose tissue (IBAT) and of bilateral adrenal demedullation on cold adaptation of rats. 2) After sympathectomy in the 28 degree C rats, there were substantial decreases in the IBAT NE basal level and turnover rate but no modifications in the heart and adrenals. In the 16 degree C rats there were also decreases in the basal level and turnover rate of the IBAT NE but, in addition, significant increases in levels and turnover rates of NE in the heart and of epinephrine in the adrenals. 3) Bilateral adrenal demedullation led to increases in the NE basal level and turnover rate in the IBAT and the heart in the 16 degree C rats; no effects were observed in the 28 degree C rats. 4) It is concluded that in rats born and reared in a mild cold environment a compensatory stimulation of catecholamine production and turnover rate occurs in some organs after a partial sympathectomy of BAT or bilateral adrenal demedullation.