Clinicopathological and cytogenetic features of two patients with acute myelogenous leukemia (AML) whose blast cells coexpressed myeloid-associated antigens and CALLA are described. Leukemia cells revealed myelomonocytic (FAB-M4) and monocytic (FAB-M5) features, while the nonblast cell population exhibited trilineage myelodysplasia in both cases, a finding suggestive of multiple-cell-lineage involvement. Cytogenetically, a deletion of the long arm of chromosome 6 was found in one patient, and normal metaphases were detected in the other. Molecular studies disclosed a rearrangement of the IgH locus in one patient. Clinically, these patients were unresponsive to antimyeloid regimens including Daunorubicin and Cytarabine, two agents normally also effective on lymphoblastic leukemias, possibly indicating the need for alternative protocols for the treatment of CALLA positive AML.