The immunological phenotypes of leukemia cell samples from 60 patients, of whom 54 had acute myeloid leukemia (AML), were assessed with a panel of monoclonal antibodies (Mabs) with specificity for the following epitopes: (i) Epitopes associated with myeloid leukemia cells, (ii) Epitopes expressed only on immature myeloid cells (or subsets) and on monocytes, (iii) Epitopes only expressed on granulocytes or on granulocytes and mature myeloid cells (promyelocytes, myelocytes and monocytes), (iv) Epitopes on HLA‐class II (DR) and (v) HLA‐class I molecules and on insulin receptors.This panel of Mabs proved useful to identify leukemia cells in blood and to assess their myeloid origin. The panel of Mabs was found also to be useful for immu‐nophenotyping of leukemia cells. Furthermore, the analysis revealed considerable variations in the immunological phenotype of AML cells, reflecting antigenic heterogeneity within the individual leukemia cell population as well as abnormal or no expression of histocompatibility antigens and insulin receptors in some samples. Some of the Mabs bound preferentially to subgroups in the French‐American‐British (FAB) class