['The aim of this study was to investigate if olympic (amateur) boxing is associated with elevation of brain injury biomarkers in peripheral blood compared to controls.', 'Thirty olympic boxers competing in at least 47 bouts were compared to 25 controls. Blood was collected from the controls at one occasion and from the boxers within 1-6 days after a bout and after a rest period of at least 14 days. Tau concentration in plasma was determined using a novel single molecule ELISA assay and S-100B, glial fibrillary acidic protein, brain-derived neurotrophic factor and amyloid β 1-42 were determined using standard immunoassays.', 'None of the boxers had been knocked-out during the bout. Plasma-tau was significantly increased in the boxers after a bout compared to controls (mean\u2009±\u2009SD, 2.46\u2009±\u20095.10 vs. 0.79\u2009±\u20090.961\u2009ng\u2009L(-1), p\u2009=\u20090.038). The other brain injury markers did not differ between the groups. Plasma-tau decreased significantly in the boxers after a resting period compared to after a bout (p\u2009=\u20090.030).'] Is olympic boxing associated with elevated levels of the neuronal protein tau in plasma?