Neurofilament light chain polypeptide (NFL), like NFM and NFH, is an important component of neurofilaments and maintains neuronal caliber. NFs are abundant proteins that are exclusively expressed in neurons, they may serve as a marker of neuronal degradation. Under normal conditions, NFL is released at low level from axons; however, this rate increases with age and following neuroaxonal damage. Therefore, abnormal, elevated levels of NFL can be detected in cerebrospinal fluid and blood in various acute and chronic neurological disorders.  Monitoring NFL levels in CSF or blood is useful in clinical diagnostic evaluations for predicting the progression of various acute and chronic neurological diseases, as well as for assessing treatment efficacy.