An important biological feature of prostate cancer (PCa) is its marked preference for bone marrow as a metastatic site. To identify factors that may support the growth of PCa in bone marrow, expression of receptor and nonreceptor tyrosine kinases by androgen-independent PCa bone marrow metastases was assessed. Bone marrow biopsies largely replaced by PCa were analyzed using reverse transcriptase-polymerase chain reaction amplification with degenerate primers that amplified the conserved kinase domain. Sequence analyses of the cloned products demonstrated expression of multiple kinases. Expression of the receptor and nonreceptor tyrosine kinases, alpha platelet-derived growth factor receptor and Jak 1, respectively, was confirmed by immunohistochemistry. In contrast, the type 1 insulin-like growth factor receptor, thought to play a role in PCa development, was lost in metastatic PCa. These results implicate several specific growth factors and signaling pathways in metastatic androgen-independent PCa and indicate that loss of the type 1 insulin-like growth factor receptor contributes to PCa progression.