To date, only anti-glycophorin-A monoclonal antibodies (MAbs) have been widely used as anti-erythroid probes in the diagnosis of leukemias. We have examined blood, bone-marrow and lymph-node samples from 474 patients, adults and children, with different hemopoietic malignancies, using a panel of MAbs including 2 anti-erythroid MAbs directed to glycophorin-A and an antigen of erythroblasts, Ag-Eb. MAb HAE9 directed against a human epitope of Ag-Eb has earlier been shown to be highly specific for immature erythroid cells. Of all the patients, 2.7% demonstrated glycophorin-A expression on blast cells, while anti-Ag-Eb MAb HAE9 reacted positively with cells from 6.0% of patients. Samples from 31 of 474 (6.5%) patients expressed one or both erythroid markers. Our results indicate that MAb HAE9 may be useful, in combination with anti-glycophorin-A MAbs, as an anti-erythroid probe for immunophenotyping human leukemias.