The aim of this study was to test the hypothesis that vascular dysfunction in neonatal streptozotocin (n-STZ)-induced diabetic rats could be associated with alterations in blood pressure, hemodynamic profile, and levels of superoxide anion. Diabetes was induced by STZ injection (160 mg/kg, i.p.) in neonate (2-d-old) Wistar rats. Using intravital microscopy the changes in mesenteric arteriolar diameters to vasoconstrictor agent noradrenaline (NA) and the levels of superoxide anion, measured by hydroethidine microfluorography, were determined in anaesthetized control and n-STZ rats. Blood pressure (BP) was determined in anaesthetized and unanaesthetized animals. Heart rate, shear rate, and blood flow velocity were also assessed. n-STZ rats showed, after 8 weeks of STZ injection, increased BP (unanaesthetized animals), hyperactivity to NA, and increased superoxide anion levels. However, heart rate, arteriolar shear rate, and blood flow velocity were unchanged in n-STZ. In conclusion, the results of the current study describe a significant increase in blood pressure, hyperactivity to NA-mediated vasoconstriction, and increased superoxide levels measured by hydroethidine oxidation. Taken together, our findings demonstrate that the compromised ability of mesenteric microvessels to respond properly in n-STZ diabetic rats is associated with several vascular alterations.