1-Methylnicotinamide (MNA), a major endogenous metabolite of nicotinamide, possesses anti-thrombotic and anti-inflammatory activity, and reverses endothelial dysfunction. In the present work, we investigated whether such a vasoprotective profile of MNA activity affords anti-diabetic action in rats. Diabetes was induced by streptozotocin (STZ) in Sprague-Dawley rats. Eight weeks after STZ injection in untreated or MNA-treated rats (100 mg kg(-1) daily), development of diabetes (plasma concentrations of fasting and non-fasting glucose, HbA(1c), peptide C), development of oxidant stress (lipid peroxidation, carbonylation of plasma proteins), as well as NO-dependent endothelial function in aorta, coronary and mesenteric vessels were analyzed. Finally, the effect of chronic treatment with MNA on long-term survival of diabetic rats was determined. Chronic treatment with MNA profoundly lowered fasting glucose concentrations in plasma, displayed mild effects on plasma HbA(1c) and peptide C concentrations, while having no effects on non-fasting glucose. On the other hand, MNA treatment considerably lowered lipid peroxidation, protein carbonylation, completely prevented impairment of endothelium-dependent vasodilatation in the aorta that was mediated entirely by NO, but failed to affect endothelial function in resistant vessels, which was mediated only partially by NO. Most importantly, chronic treatment with MNA prolonged the long-term survival of diabetic rats. In conclusion, MNA displayed a significant anti-diabetic effect that may be linked to its vasoprotective activity.