Two closely related protein-tyrosine kinases with the characteristics of growth factor receptors were identified by screening a chicken embryo cDNA expression library with anti-phosphotyrosine antibodies and were designated Cek2 and Cek3 (chicken embryo kinases 2 and 3). Cek2 and Cek3 are structurally related to Cek1, a chicken basic fibroblast growth factor receptor, and presumably represent receptors for basic fibroblast growth factor-related molecules. The identification of Cek2 and Cek3 establishes the existence of a family of protein-tyrosine kinases that includes Cek1 and that is likely to be implicated in the control of developmental processes. Among protein-tyrosine kinases, this family of receptors, which may include other as yet unknown members, is most closely related to the protooncogene product Ret and the platelet-derived growth factor receptor family.