The morphologic characteristics of bone marrow aspirates from patients recovering from acute agranulocytosis may be closely similar to the pattern observed in cases of acute promyelocytic leukemia (APL). The clinical manifestation also can be ambiguous in a substantial number of cases. The immunophenotypic features of bone marrow from 5 patients recovering from acute agranulocytosis, showing an increase in the percentage of promyelocytes (26%-66%), were compared with the immunophenotype of 31 consecutive patients with APL whose diagnosis was confirmed by PML-RAR alpha gene rearrangement. All markers were similarly expressed, except for CD117 and CD11b. CD117 was positive in 24 (77%) of the APL cases and in none of the acute agranulocytosis cases. On the other hand, CD11b was positive in 5 (100%) of the acute agranulocytosis cases and in only 2 (6%) of the APL cases. Thus, the CD117-CD11b+ phenotype was detected in all patients recovering from agranulocytosis and in only 1 (3%) of 31 APL cases. Therefore, we suggest that the combination of both markers is helpful in the differentiation of APL from recovering benign myeloid proliferation.