The present invention relates to a biomarker for the detection of brain damage or a disease associated with loss of neurons, said biomarker comprising a protein fragment of the neurofilament heavy chain (NfH) protein in a biological sample, wherein said protein fragment is a polypeptide selected from the group consisting of i) a polypeptide having the amino acid sequence selected from the group consisting of SEQ ID NO:1, SEQ ID NO:2, SEQ ID NO:3, SEQ ID NO:4, SEQ ID NO:5, and polypeptides composed of amino acids 476-1026 and 476-986 of SEQ ID NO 6; ii) a protein fragment of the NfH protein having an amino acid sequence that is at least 60% identical to SEQ ID NO:1, at least 60% identical to SEQ ID NO:2, at least 60% identical to SEQ ID NO:3, at least 60% identical to SEQ ID NO:4, at least 60% identical to SEQ ID NO:5; or at least 60% identical to a polypeptide composed of amino acids 476-1026 and.or 476-986 of SEQ ID NO 6; iii) an Enterokinase cleavage product of the NfH protein; and iv) a polypeptide that is derived from a naturally occurring allelic variant of the nucleic acid coding for NfH protein.