Neurofilaments, a major cytoskeletal constituent of neuronal cells, can be released into the cerebrospinal fluid during several neurodegenerative diseases. By means of a new sensitive ELISA capable of measuring 60 ng/l of neurofilament light, significant elevations were observed for different neurological disorders. Cerebral infarction presented levels of 19800+/-9100 ng/l, amyothropic lateral sclerosis 3600+/-1200 ng/l, 'relapsing-remitting' MS 2500+/-1500 ng/l, extrapyramidal symptoms 1100+/-300 ng/l, late onset AD 300+/-100 ng/l and vascular dementia 1400+/-800 ng/l. In patients with no signs of neurological diseases the upper normal level and cut-off values was determined to be below 100 ng/l. NF-L determinations will be a valuable complement in identifying neuronal degradation and can be used clinically for diagnostic and monitoring purposes.