Endothelial dysfunction is an early marker of atherosclerosis. Pioglitazone is commonly used in the treatment of type 2 diabetes and has vascular protective effects beyond its hypoglycemic ones. We investigated the vascular effects of short-term, low-dosage pioglitazone in patients with type 2 diabetes. The study included 15 subjects with type 2 diabetes with normoalbuminuria (age, 60.7 +/- 11.9 years; body mass index [BMI], 23.9 +/- 3.3 kg/m2). The patients received pioglitazone at 15 mg daily for 4 weeks. BMI, systolic and diastolic blood pressure, laboratory parameters (fasting plasma glucose, insulin, lipid profile, high-sensitive C-reactive protein [hsCRP], and adiponectin) were assessed at baseline and after treatment. The forearm blood flow (FBF) was measured during reactive hyperemia by strain-gauge plethysmography. Short-term, low-dosage pioglitazone did not improve glycemic control or insulin sensitivity. However, the peak FBF and flow debt repayment (FDR) were markedly improved. There was no correlation of the improvement of peak FBF and FDR with the observed changes of metabolic parameters. However, the increment of adiponectin and decrement of hsCRP were well correlated with the improvement of peak FBF. These results indicate that short-term low-dosage pioglitazone may improve vascular function via increasing adiponectin expression and decreasing low-grade inflammation in type 2 diabetic patients.