Neurofilaments (NFs) belong to the family of intermediate filaments (IFs) and are structural elements of the neuronal cytoskeleton in an interconnection with actin microfilaments, microtubules and other IFs. NFs are composed of three different subunits that are different, but related proteins: NF-L (70 kDa), NF-M (150-160 kDa) and NF-H (200 kDa). The antigenic determinants of each of the subunits may be unique or shared and each NF subunit is a separate gene product. During embryonic neurogenesis, the NF-L and NF-M subunits are coexpressed, whereas the activation of the NF-H subunit is delayed to the postnatal period. NF-M and NFH subunits are unable to self-assemble and, typically, form co-polymers with NF-L.