UT-7 is a human megakaryoblastic leukemia cell line with absolute dependence on interleukin-3, granulocyte-macrophage colony-stimulating factor (GM-CSF), or erythropoietin (EPO) for growth and survival. We isolated a novel subline, UT-7/GM after long-term culture of UT-7 with GM-CSF. The hemoglobin concentration and γ-globin and EPO-receptor mRNA levels were significantly higher in EPO-treated UT-7/GM cells than in untreated cells. In contrast, the platelet factor 4 and glycoprotein lib mRNA levels were much higher in thrombopoietin (TPO)-treated UT-7/GM cells than in untreated cells. Some TPO-treated cells had morphologically mature megakaryocytic characteristics such as a developed demarcation membrane in the cytoplasm and multilobular nuclei. These findings indicate that UT-7/GM is a bipotential cell line that can be induced to differentiate into erythroid and megakaryocytic lineages by EPO and TPO, respectively. Moreover, a minority of UT-7/GM cells acquired a high hemoglobin concentration by treatment with TPO, suggesting that TPO in part induced the erythroid differentiation of the UT- 7/GM cells. Interestingly, GM-CSF inhibited the EPO- or TPO-induced erythroid differentiation and the TPO-induced megakaryocytic differentiation of UT- 7/GM cells. These results support the hypothesis that cytokines influence the programming of gene expression required for lineage commitment or differentiation.