Autologous blood doping, in which an athlete is transfused with their own stored red blood cells to increase their oxygen capacity for competition, might be detectable now with the use of a microRNA marker of blood aging. An 18-nucleotide miRNA called miR-720 is produced in a predictable pattern as blood ages, which would allow sports officials to detect this kind of blood doping for the first time. The finding might also improve blood storage.