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Autonomous colony formation is a frequent event in erythroleukemia. In 13 cases of early erythroid leukemias, we investigated whether erythropoietin (Epo) autocrine stimulation was responsible for the growth factor autonomy. Epo transcripts were detected by Northern blotting in cells from one patient. These cells also expressed an Epo receptor (1,000 receptors per cell) with a 420-pM affinity and Epo was detected in the supernatant of cultured cells. In 8 of the 13 cases, Epo transcripts were revealed by the polymerase chain reaction ranging from 0.5 to 500 copies per cell. In situ hybridization proved that these Epo transcripts were present in the blast cells. No Epo gene abnormalities were detected by Southern blotting. In two cases, leukemic cells were grown in the presence of Epo-neutralizing antibodies or Epo antisense oligomers. In one case, the antibody significantly reduced autonomous growth. In contrast, the antibody had no effect in the second case in which blast cells transcribed the Epo gene at a low level. However, Epo antisense oligomers partially inhibited autonomous growth. This inhibition was reversed by addition of exogenous Epo. Overall, these results suggest that an extracellular or intracellular autocrine Epo stimulation occurs in some cases of erythroid malignancies.