An improved, simplified method for the demonstration of the adrenergic innervation to the heart based on perfusion fixation is described. After perfusion with phosphate-buffered paraformaldehyde, specimens of heart tissue are frozen on Dry Ice, cut in the cryostat at –10°C and exposed to formaldehyde gas at 80°C for 30 min. The perfusion solution limits diffusion and makes it possible to show catecholamine fluorescence in cryostat sections of the heart of a quality heretofore only possible in freeze-dried tissue. The elimination of the need for freeze-drying allows studies of the effects of drugs or other procedures to be carried out in a single day with relatively simple equipment. Fixation by the perfusion solution used has been shown to be compatible with modern neurohistologic methods and to be of good quality for studies of ultrastructure. When perfused tissues are freeze-dried, catecholamine fluorescence of high quality, fully comparable to that possible with nonperfused tissue, is found. Freeze-drying of perfused heart eliminates the necessity and value of exposure to paraformaldehyde gas.