Oxidative stress and low-grade inflammation are hallmarks of diabetes mellitus. We explored protective, blood pressure-independent effects of the angiotensin II type 1 (AT(1)) receptor antagonist candesartan and the selective beta(1)-adrenoceptor antagonist metoprolol. Diabetes mellitus was induced in 8-week-old Sprague-Dawley rats after injection of streptozotocin. Diabetic rats were randomized to treatment with candesartan or metoprolol in sub-antihypertensive doses or to placebo treatment. In the quadriceps, musculature markers of oxidative stress and inflammation were determined. Function of the inherent vascular bed was measured in vivo in the autoperfused hindlimb. Increases in NAD(P)H activity, expression of its cytosolic subunit p22(phox) and of endothelial NO synthase e(NOS) displayed enhanced oxidative stress. Upregulated intercellular (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 and of inducible NOS (iNOS) revealed inflammatory processes. Diabetes was associated with severe impairment of endothelium-dependent and -independent vasodilatation. Candesartan, but not metoprolol, reduced NAD(P)H activity, attenuated diabetes-induced over-expression of p22(phox) and eNOS mRNA as well as ICAM-1, VCAM-1, iNOS and eNOS immunoreactivity and led to a substantial improvement of endothelium-dependent vasodilatation (+46.3% vs. placebo treatment; P<0.05). Angiotensin AT(1) receptor antagonism, but not beta(1)-adrenoceptor antagonism, ameliorates diabetes-generated oxidative stress, indicating a pivotal role of the renin-angiotensin system in the development of diabetic complications.