Plasma leakage is a phenomenon which has almost completely disappeared since the introduction of plasma-tight polymethylpentene (PMP) fibers in oxygenators used for extracorporeal life support (ECLS). We describe here a case of ECLS which was affected by the rapid occurrence of plasma leakage in oxygenators with polymethylpentene fibers. To our knowledge, this is the first report of the phenomenon since the introduction of this new generation of oxygenators.