Rapid nerve conduction in vertebrates depends on myelin’s ensheathment of axons. Conduction abnormalities and severe debilitation is due to de-, dys-, and a- myelination. Electron microscopy can provide an essential description of myelin morphology, but compared to diffraction lacks the requisite resolution, sampling, and non-invasiveness to delineate molecular organization and dynamic interactions. About 40 years ago, we showed the complementarity of neutron diffraction (ND) to x-ray diffraction (XRD) for myelin structural studies. Over the last several years at the ILL, we have revisited the applicability of ND to structural analysis of myelin. Using PNS nerves, we demonstrated a vast improvement in temporal and spatial resolution of current instrumentation. We also recorded meaningful data from CNS myelin for the first time and used real-time H-D exchange measurements to characterize myelin from a transgenic animal. We propose now to explore the use of in vivo labeling techniques to incorporate D directly into myelin membrane components. These studies will examine the localization of (1) deuterated cholesterol and (2) non-specifically deuterated membrane components in myelin.