Background— Peroxisome proliferator–activated receptor-γ (PPAR-γ) agonists inhibit vascular smooth muscle proliferation and migration and improve endothelial function. It is unknown whether PPAR-γ agonists favorably modulate bone marrow (BM)–derived angiogenic progenitor cells (APCs) to promote endothelial lineage differentiation and early reendothelialization after vascular intervention. Methods and Results— C57/BL6 mice, treated with or without rosiglitazone (8 mg/kg per day), a PPAR-γ agonist, underwent femoral angioplasty. Rosiglitazone treatment attenuated neointimal formation (intima/media ratio: 0.98±0.12 [rosiglitazone] versus 3.1±0.5 [control]; P <0.001; n=10 per group). Using a BM transplantation model, we identified that 58±12% of the cells within the neointima at 4 weeks were derived from the BM. Pure endothelial marker–positive, pure α-smooth muscle actin (αSMA)–positive, or double-positive APCs could be found both in mouse BM and in human peripheral blood after culture in conditional medium enriched with vascular endothelial growth factor. Rosiglitazone caused a 6-fold ( P <0.001) increase in colony formation by human endothelial progenitor cells, promoted the differentiation of APCs toward the endothelial lineage in mouse BM in vivo (0.66±0.06% [control] to 0.95±0.08% [rosiglitazone]; P <0.05) and in human peripheral blood in vitro (13.2±1.5% [control] to 28.4±3.3% [rosiglitazone]; P <0.05), and inhibited the differentiation toward the smooth muscle cell lineage. Within the neointima, rosiglitazone also stimulated APCs to differentiate into mature endothelial cells and caused earlier reendothelialization compared with controls (31±5 versus 8±2 CD31-positive cells per millimeter of neointimal surface on day 14; P <0.01). Conclusions— Similar to embryonic stem cell–derived progenitors, the adult BM and peripheral blood harbor APCs that are at least bipotential and able to differentiate into endothelial and smooth muscle lineages. The PPAR-γ agonist rosiglitazone promotes the differentiation of these APCs toward the endothelial lineage and attenuates restenosis after angioplasty.