Norepinephrine uptake and turnover rate were measured in the interscapular brown adipose tissue of normal and hypothyroid young rats. At the age of 15 days, hypothyroidism lowers the uptake of norepinephrine. This fact could partially explain why the norepinephrine content of the tissue has previously been found reduced in these animals when compared to controls. In the same animals, the turnover rate of norepinephrine is reduced by 80%. This indicates a decrease of the sympathetic tonus in the tissue.