We have cloned a murine cDNA on the basis of homology to the tyrosine kinase domain of the bek fibroblast growth factor receptor. This cDNA encodes a putative tyrosine kinase receptor with a unique structural pattern in its extracellular domain. It is a new member of the immunoglobulin superfamily with two immunoglobulin-like domains. It also contains two fibronectin type III domains which are found on diverse proteins such as receptor tyrosine phosphatases and neural cell adhesion molecules. This protein tyrosine kinase called ark (adhesion-related kinase) is likely to represent a new class of receptor tyrosine kinase. Ark mRNA appears to be expressed in most cell lines and adult tissues examined except those of hematopoietic lineage. It is undetectable in undifferentiated teratocarcinoma cells, F9 and N Tera 2.