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Myeloblasts are approximately 15-20 microns in size, and have high nuclear to cytoplasmic ratios.  The nucleus is usually round to oval, but may be irregular.  The chromatin is smooth and open, and one or more nucleoli may be present.  The cytoplasm is pale blue.  Cytoplasmic granules are not typically seen, though rare small granules may be present.  Leukemic myeloblasts may contain few cytoplasmic granules or Auer rods, which are reddish, linear structures composed of fused primary granules.  The presence of Auer rods indicates myeloid malignancy.