AXL is a member of the receptor tyrosine kinase family which has oncogenic potential and is implicated in human myeloid leukemia. AXL is a member of a complex signaling network th at is involved in the control of cell proliferation and differentiation. Overexpression of AXL cDNA in NIH 3T3 cells induces neoplastic transformation of these cells with the concomitant appearance of a 140 kDa AXL tyrosine-phosphorylated protein. Expression of AXL cDNA in the baculovirus system results in the expression of the appropriate recombinant protein th at is recognized by antiphosphotyrosine antibodies, confirming th at the AXL protein is tyrosine phosphorylated.