Experiments were performed on brains of white Wistar rats, of both sexes, weighing 180-200g and 24 cats from various sources. Frontal sections were fixed in Backer's formalin and thereafter cut in a cryostat on 10 microns thick slices, dried on air. The slices were: a) either preincubated 1 hr in room temperature in solutions of the following amines: adrenaline, noradrenaline dopamine and L-dopa, para amino-diphenylamine and its derivatives, thereafter incubated in an incubation medium which conatained nitro-BT, phenazine-methosulfate (PMS), and glycine-buffer pH 9-5 b) or simultaneously incubated with the above mentioned standard medium. It has been found that all compounds tested, enhanced the reaction significantly in the fibers of the central nervous system except L-dopa. The last compound underwents very intensive autooxidation so that its influence on the reaction could not be taken into account. The observed reaction results allow us to suggest that the oxidation-reduction reaction in the nerve fibers might be of significance in the catabolism of biogenic amines.