Representative appearance of a portion of a PMN that appeared in a culture of nonleukemic bone marrow mononuclear cells incubated in the presence of ATRA for 1 week. Both MPO-positive and -negative (arrow) cytoplasmic granules are present, with the former outnumbering the latter. Large spherical lipid droplets (L) are also present. N, nucleus. (MPO-stained section, original magnification × 17,700.)