In tumors, new blood vessels develop not only from pre-existing vessels (angiogenesis), but can also be comprised of circulating vascular progenitor cells originating from the bone marrow (vasculogenesis). Besides endothelial progenitor cells (EPC) and pericyte progenitor cells (PPCs) that are incorporated into the growing vasculature, other subpopulations of bone marrow-derived cells (BMDC) contribute indirectly to tumor neovascularization by providing growth factors, cytokines, and other key proangiogenic molecules. Here, we describe specific methods that allow for the identification and functional characterization of these distinct BMDC populations in tumors as exemplified in mouse models of pancreatic neuroendocrine tumors and glioblastomas.