The long-distance effects of brain lesions: visualization of myelinated pathways in the human brain using polarizing and fluorescence microscopy. We describe several new possibilities for the study of degenerated myelinated tracts in the human central nervous system (CNS). The methods are based on the visualization of myelin breakdown products that show birefringence in polarized light and, when stained with Nile blue and benzpyrene-3,4, exhibit fluorescence. Even after lengthy formalin fixation, the methods permit the localization of anterogradely degenerated tracts in a variety of fiber systems in the brains of patients who died between five and 20 months after the onset of neurological symptoms. Particularly the polarizing technique, because of its simplicity, can be added to the usual neuropathological methods for demonstrating the long-distance effects of a brain lesion. As research tools, these methods would also aid in the study of the anatomical substrate of human neurological symptomatology. 