In post-ganglionic sympathetic neurons, biochemical and electron-microscopical evidence indicate that noradrenaline is stored within granules which, although smaller, resemble adrenal medullary chromaffin granules in some respects. This resemblance between neuronal and adrenal medullary granules has been extended by immunological and enzymic investigations which show that sympathetic nerve granules contain the proteins chromogranin A and dopamine β-hydroxylase which characteristically occur in chromaffin granules.