Neurofilament light (NfL) is a 68 kDa cytoskeletal intermediate filament protein that is expressed in neurons. It associates with the 125 kDa Neurofilament medium (NfM) and the 200 kDa Neurofilament heavy (NfH) to form neurofilaments. They are major components of the neuronal cytoskeleton, and are believed to function primarily to provide structural support for the axon and to regulate axon diameter. Neurofilaments can be released in significant quantity following axonal damage or neuronal degeneration. NfL has been shown to associate with traumatic brain injury, multiple sclerosis, frontotemporal dementia and other neurodegenerative diseases. The Simoa NF-light™ assay is a digital immunoassay for the quantitative determination of NfL in serum, plasma and CSF. The antibodies also cross react with murine, bovine, and macaque NfL epitopes, and the assay can be used for research with these species.