The rate of oxygen consumption measured at 32.5 degrees C of lightly anesthetized 129/ReJ dy/dy mice was greater than that of dy/+ or +/+ control mice. However, the norepinephrine-stimulated rates of oxygen consumption of dystrophic and normal mice were similar. Brown adipose tissue cellularity (DNA content) of dystrophic mice was unchanged, and the tissue protein and succinate dehydrogenase contents were slightly reduced. The mitochondrial concentration of the uncoupling protein, thermogenin, and purine nucleotide binding to mitochondria isolated from brown fat of normal or dystrophic mice, were similar. These results indicate that the nonshivering thermogenic capacity of dystrophic mice is not significantly altered.