Bone marrow stromal cells (MSCs) are pluripotent cells capable of differentiation into several tissue types. This present study was performed to determine their functional neoangiogenic potential in vivo. Whole bone marrow was harvested from C57Bl/6 mice, and the adherent cellular fraction was culture expanded for 14 doublings. These MSCs were resuspended in Matrigel and their angiogenic effect assessed in isogenic recipients. At 2 weeks postimplantation, the mean vascular density in Matrigel plugs containing 2× 10 6 MSCs/ml was 41±5.0 blood vessels (BVs)/mm 2 compared to 0.5±0.7 for empty Matrigel (P< 0.001). In comparison, Matrigel plugs containing either recombinant murine VEGF 165 at 50 ng/ml or bovine bFGF at 1000 ng/ml generated 21±5 and 11±2.0 BV/mm 2, respectively. Arteriogenesis was observed only in the MSC-containing implants. With the use of LacZ retroviral labeling of ex vivo expanded MSCs, we show that∼ 10% of LacZ+ MSCs differentiated into CD31+ and VEGF+ endothelial cells. More than 99% of the neoangiogenic phenomena arose from recruitment of host-derived LacZ null vascular structures. Neutralizing anti-VEGF antibodies inhibited the MSC-initiated angiogenic response in vivo by 85%(P< 0.001). In conclusion, MSCs have the ability to effectively recruit and participate in angiogenesis and arteriogenesis de novo and VEGF plays a central role in the observed host-derived angiogenic response. We propose that ex vivo expanded autologous MSCs may serve as cell therapy to promote therapeutic angiogenesis.