Factors that bind and activate receptor tyrosine kinases are known to play key roles during development and in the adult. The Eph-related receptors constitute the largest known family of receptor tyrosine kinases. Members of the Eph family exhibit intriguing patterns of expression in the embryo, implicating them in a variety of developmental processes, and their expression is often restricted to particular subpopulations of postmitotic neurons in the adult. We describe the identification and characterization of a novel member of the Eph receptor family, which we have termed Ehk-3 for Eph Homologous Kinase 3. Ehk-3 displays all the major structural features shared by other members of the Eph family, including a cysteine-rich region and tandem fibronectin type-III domains in its extracellular portion. Ehk-3 is expressed in two forms in a developmentally-regulated fashion: a conventional full-length version containing the intracellular tyrosine kinase domain, as well as a truncated form that lacks this domain. Both forms of Ehk-3 are quite restricted to the nervous system in the adult, but Ehk-3 is more widely expressed in the embryo, suggesting that Ehk-3 mediates different functions during development and in the adult.