DAWKINS et al.1 have presented results of an investigation of the localization of catecholamines in brown fat, in which they used the histochemical fluorescence method of Falck and Hillarp2,3. They found a distinct fluorescence within the cytoplasm of the brown fat cells and in nerve fibres of the parenchyma. The fluorescence was reported to be abolished when the sections were treated with sodium borohydride and to be very weak or absent in tissue samples from reserpinized animals. Thus this fluorescence was assumed to indicate the presence of noradrenaline both in the nerve fibres and in the cytoplasm of the brown fat cells.