Granulocyte macrophage colony-stimulating factor, interleukin-3, and steel factor induce proliferation of hematopoietic cells through binding to specific, high affinity, cell surface receptors. However, little is known about post-receptor signal transduction pathways. Here we report that an SH2 domain containing protein previously implicated in the activation of p21ras, Shc, is transiently tyrosine phosphorylated in myeloid cells after stimulation with granulocyte macrophage colony-stimulating factor, interleukin-3, or steel factor. Also, Shc was found to be constitutively tyrosine phosphorylated in myeloid cell lines made factor independent by expression of p210BCR/ABL. A Shc-associated 140-kDa protein was identified, which was phosphorylated on tyrosine residues transiently after cytokine stimulation and constitutively after expression of p210BCR/ABL. These findings suggest that Shc could play an important role in a signal transduction pathway, which leads to the proliferation of myeloid cells.