Examination of tau levels in patients 24 h after cardiac arrest shows that phosphorylated‐tau (p‐tau) increases rapidly in the short term, suggesting that p‐tau is secreted rapidly in the interstitial fluid after hypoxic–ischemic brain injury rather than continuously as NFL or total‐tau (t‐tau), while Aβ42 and Aβ40 concentrations increased over time in most patients but only weakly. The gene discussed is MAPT; the disease is cardiac arrest.