The aim of this study was to assess the effect of rosiglitazone on endothelial function of the coronary arteries and on plasma levels of inflammatory markers in diabetic patients with coronary artery disease (CAD). Fifty-six patients with type 2 diabetes and CAD were randomized to receive either rosiglitazone (4 mg/day) or a control for 12 weeks. The coronary flow velocity reserve (CFVR) was assessed using transthoracic Doppler echocardiography at baseline and after 12 weeks. After 12 weeks of rosiglitazone treatment, plasma levels of C-reactive protein were significantly decreased and the median CFVR was significantly increased compared with baseline levels and compared with the control group. These results suggest that, in addition to its beneficial metabolic effects, rosiglitazone, via its anti-inflammatory effects, may improve endothelial function of the coronary arteries in patients with diabetes and CAD.