Neurofilaments are the 10nm or intermediate filament proteins found specifically in neurons, and are composed predominantly of three major proteins called NF-L, NF-M and NF-H. NF-M is the neurofilament middle or medium molecular weight polypeptide and runs on SDS-PAGE gels at 145-160kDa, with some species variability, though the real molecular weight is ~105kDa. The major function of neurofilaments is likely to control the diameter of large axons (1). Antibodies to NF-M such as MAB-10583are useful for identifying neuronal cells and their processes in tissue sections and in cell culture. NF-M antibodies can also be useful to visualize neurofilament rich accumulations seen in many neurological diseases, such as myotrophic Lateral Sclerosis (a.k.a. Lou Gehrig’s disease) and Alzheimer’s disease (2-4). Much recent evidence has suggested that the detection of NF-L and NF-H in blood and CSF might be a useful prognostic or diagnostic biomarkers of neuronal damage and degeneration associated with a variety of CNS pathologies (5,6). The potential utility of NF-M in this fashion has not to date been examined. The MAB-10583antibody was made against a recombinant fusion protein of E. coli TrpE fused to the C-terminus of rat NF-M, amino acids 677-845 (7). The epitope was mapped using protein cleavage to the extreme C-terminal sequence, amino acids 762-845, a region of very conserved protein sequence which includes some interesting sequence repeats of currently unknown function (8). This epitope corresponds to amino acids 833-916 of the slightly larger human NF-M sequence. The antibody works on a variety of species and is clean on western blots of crude lysates, on cells in culture and staining of sectioned material. The antibody has been widely used for many years, for example the original observation that the widely used HEK293 cell line has unexpected neuronal properties was made with this antibody (9).