Stomatocytic transformation of red blood cells after marathon running.

We studied red blood cell morphology in two marathon runners before, immediately after, and 1 day after a marathon race. A discocyte-stomatocyte transformation was found by light microscopy of wet preparations and also by scanning electron microscopy, with about one-half the erythrocytes becoming cup-shaped after the marathon. These changes were completely reversible within 18 hr after the race.