Peroxisome proliferator-activated receptors (PPARs) are expressed on vascular tissue. To investigate the direct vasoprotective effects of PPARγ and PPARα ligands, pioglitazone (3 mg/kg/day) and bezafibrate (10 mg/kg/day) were given by gavage to streptozotocin-induced diabetic rats for 4 weeks. Streptozotocin (65 mg/kg, i.p.) significantly increased NADPH oxidase, vascular call adhesion molecule-1 (VCAM-1), and osteopontin mRNA levels in the aorta, as determined by reverse transcription (RT)-polymerase chain reaction (PCR). Immunohistochemical analysis revealed that the expression of osteopontin protein was also enhanced in the streptozotocin-injected rat aorta. Pioglitazone or bezafibrate attenuated the streptozotocin-induced increase in the expression of NADPH oxidase and VCAM-1 mRNA. The enhanced expression of osteopontin gene and protein induced by streptozotocin was suppressed by pioglitazone, whereas treatment with bezafibrate had no effect on the expression of osteopontin. We also demonstrated that pioglitazone or bezafibrate prevented the streptozotocin-induced increase in angiotensin converting enzyme (ACE) gene and protein content, by the means of RT-PCR and Western blotting. On the other hand, the treatment of pioglitazone or bezafibrate in the present study did not affect glucose tolerance, serum insulin or lipid level in streptozotocin-induced diabetic rats. These results suggest that the direct anti-oxidant and anti-inflammatory effects of PPARs ligands in the aorta of streptozotocin-induced diabetic rats were not likely to have been mediated by the normalization of glucose or lipid metabolism, but instead these salutary effects appear to have been associated with the inhibition of the expression of ACE. In addition, pioglitazone appeared to be more effective on the suppression of osteopontin expression compared with bezafibrate.