Neurofilaments are 10nm intermediate filament proteins located in vertebrate neurons, which regulate axonal diameter. They are composed predominantly of the three major neurofilament proteins: NF-Light, NF-Medium and NF-Heavy. NF-M is the middle or medium neurofilament subunit and runs on SDS-PAGE gels in the range 145-170kDa, with some size variation in across species.

Antibodies to NF-M may be used to identify NF-M in neurons and to study neuronal processes in tissue sections and/or culture. NF-M can also be useful in studies of neurofilament accumulations seen in many neurological diseases, such as Lou Gehrig's disease or Alzheimer's disease.