In this study, we report a novel differential nitric oxide interaction with nonglycosylated and glycosylated hemoglobin. After in vitro incubation of hemoglobin with S-nitroso N-acetyl penicillamine (SNAP), S-nitrosoglutathione, or S-nitrosocysteine, S-nitrosylation was significantly higher in human glycosylated hemoglobin purified from diabetic subjects compared to nondiabetic controls. Inversely, spontaneous decomposition was significantly lower for S-nitrosohemoglobin obtained from glycosylated hemoglobin. Bidimensional isoelectric focusing of hemoglobins incubated in vitro with SNAP also revealed a greater interaction of nitric oxide with glycosylated hemoglobin. In addition, a significantly higher level of S-nitrosohemoglobin was found in erythrocyte lysates from streptozotocin-induced diabetic rats compared to control rats. We suggest that highly glycosylated hemoglobin in diabetic subjects may favor S-nitrosylation, which may in turn impair vascular function, and participate in diabetic microangiopathy.