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In the present work, we analyzed whether endogenous and/or transplanted bone marrow mononuclear cells (BMMC) migrate spontaneously to the crushed sciatic nerve and whether they transdifferentiate into Schwann cells (SC) in order to help repair the damaged tissue. We also studied both the immunohistochemical evolution of myelin proteins MBP and P0 and the myelin composition of both the proximal and distal stumps of the crushed sciatic nerve to determine the demyelination–remyelination period. Immunohistochemical analysis of crushed animals showed that the degeneration process consists of loss of nerve fiber integrity accompanied by degradation of myelin basic proteins MBP and P0, which is anticipated by protein cluster formation. The remyelination process appears as a recovery in nerve fiber structure as well as in MBP and P0 immunoreactivity; results obtained studying isolated myelin from the crushed sciatic nerve show a strong correlation between them. As opposed to demyelination, axonal damage is observed for a short period of time and takes place mostly in the crush area and the segments adjacent to the lesion. Evidence of spontaneous migration of endogenous or intravascularly transplanted BMMC (CD34+ and vimentin+) is found during the demyelination period exclusively to the injured sciatic nerve. Once migration takes place, transdifferentiation to SC is observed. Such migration and transdifferentiation processes might be inferred to constitute a spontaneous repair mechanism after nerve injury. © 2011 Wiley-Liss, Inc.