Accumulating evidence suggests that circulating progenitors contribute to vascular healing and remodeling under physiological and pathological conditions. Although there is growing enthusiasm for therapeutic and diagnostic application of bone marrow-derived progenitors, there are concerns that transplanted precursors or bone marrow cells may participate in the pathogenesis of unfavorable diseases such as cancer, retinopathy, and atherosclerosis. This review summarizes recent findings obtained from animal models to examine the roles of circulating vascular progenitor cells in angiogenesis, pulmonary hypertension, and vascular healing.