The immunophenotypically immature SPCs of AML and MDS-RAEB samples had the lowest ROS levels but the overall ROS profile was less heterogeneous compared to normal; the CD34+CD38high (GMP-like in particular) and CD34−AML ‘mature’ blasts were both lower in ROS than the immunophenotypic equivalent control SPCs. Here, CD34 is linked to myelodysplastic syndrome.