Recent studies have found that bone marrow-derived cells give rise to endothelial cells during states of tissue repair and disease. We have found that one key integrin, integrin-α4β1, promotes the homing of circulating endothelial progenitor cells (EPCs) to sites of ongoing tissue repair. This integrin facilitates the adhesion of EPCs to the vascular endothelium in inflamed tissue or within tumors. We demonstrate how to identify, isolate, purify, and characterize EPCs. We also demonstrate in vivo analysis of the roles of bone marrow-derived cells in tumor growth and angiogenesis by demonstrating adoptive transfer, bone marrow transplantation, tumor models, and immunohistochemistry for markers of blood and endothelial vessels. Finally, we show how to characterize cell adhesion mechanisms regulating bone marrow-derived progenitor cell trafficking.