Abstract—Peroxisome proliferator-activated receptor-&ggr; (PPAR&ggr;) ligands are widely used in patients with insulin resistance and diabetes. Because coronary artery disease is a major complication for such patients, it is important to determine the effects of PPAR&ggr; activation on arteriosclerosis. Long-term inhibition of endothelial NO synthesis by administration ofN&ohgr;-nitro-l-arginine methyl ester (L-NAME) to rats induces coronary vascular inflammation (monocyte infiltration, monocyte chemoattractant protein-1 [MCP-1] expression) and subsequent arteriosclerosis. We examined the effects of pioglitazone (a PPAR&ggr; ligand) in this rat model to determine whether PPAR&ggr; activation with pioglitazone inhibits arteriosclerosis by its indirect effects on metabolic conditions or by direct effects on the cells participating to the pathogenesis of arteriosclerosis. We found that pioglitazone did not affect metabolic states, systolic blood pressure, or serum NO levels, but did prevent the L-NAME–induced coronary inflammation and arteriosclerosis. Pioglitazone did not reduce local expression of MCP-1 but markedly attenuated increased expression of the MCP-1 receptor C-C chemokine receptor 2 (CCR2) in lesional and circulating monocytes. PPAR&ggr; activation with pioglitazone prevented coronary arteriosclerosis, possibly by its antiinflammatory effects (downregulation of CCR2 in circulating monocytes). Inhibition of the CCR2-mediated inflammation may represent novel antiinflammatory actions of pioglitazone beyond improvement of metabolic state.