Abstract
Bone marrow smears from 6 untreated patients with acute promyelocytic leukemia (APL) and 6 patients with leukemoid reactions (LR) were compared with smears from healthy controls. The mitotic indices of the granulopoietic precursor cells were significantly lower in the APL group and significantly higher in the LR group, both compared with normals. Mitotic countings seen to be of diagnostic value for distinguishing APL from conditions simulating this disease.