A 3% solution of potassium permanganate is effective at acid pH as a fixative for the small noradrenaline-containing granular vesicles of the symapthetic nervous system. The observed high electron density of the central granules in the vesicles is probably due to precipitated MnO₂ which is reduced KMnO₄ in a coupled oxidation of noradrenaline to noradrenochrome. A 3% solution of KMnO₄ in dichromate buffer (pH 6.0) is particularly suitable for the fixation of the vesicles. This may be due to the additional precipitation of a chromic compound reduced from the dichromate.