In order to provide a further control a case of acute agranulocytosis was also investigated, in which > 75% bone marrow cells were arrested at the promyelocyte stage; these bone marrow cells showed a surface phenotype identical to non-leukemic promyelocytes (CD11a+, CD11b+, CD15+, CD45R0+, CD45RA-) with a spontaneous ability to differentiate in vivo towards the more mature stages of myeloid differentiation.