Vascular response was assessed in rats made diabetic by subtotal pancreatectomy (PPx). Adult male Wistar rats submitted to PPx eight weeks earlier, and exhibiting altered levels of fasting glucose and an abnormal tolerance glucose test, were used. Sham-operated laparotomized rats were employed as controls. Dose-response curves for acetylcholine-induced, endothelium-related relaxation of aortic rings (after previous exposure to phenylephrine) were conducted in a high glucose solution (44 mmol/L). PPx decreased significantly acetylcholine-induced relaxation only in the presence of a high glucose solution (p<0.00001). Tiron, superoxide dismutase (SOD) or melatonin restored altered aortic relaxation. Melatonin, SOD or Tiron were equally effective in restoring the impaired sodium nitroprusside-induced vasorelaxation in endothelium-denuded aortic rings of PPx rats. The results support the evidence about the ability of antioxidants to restore altered vascular reactivity of aortic rings in PPx rats, probably through the scavenging property of superoxide anion accumulation.