Background: It is controversial whether the change in nitric oxide (NO) expression in the dorsal root ganglia (DRG) may be responsible for developtment and/or maintenance of painful diabetic neuropathy. The aim of this study was to clarify the role of NO in the pathogenesis of painful diabetic neuropathy. Methods: The effect of L-nitroargine methylester (L-NAME) or sodium nitroprusside (SNP) on allodynia was measured in streptozotocin (STZ)-induced diabetic rats. NO concentration was measured in the cerebrospinal fluid (CSF) and plasma of the diabetic rats. NADPH-diaphorase (NADPH-d) histochemistry was performed on the DRG and spinal cords of the STZ-induced diabetic rats. Results: L-NAME, an inhibitor of nitric oxide synthase, alleviated allodynia, while SNP, a nitric oxide donor, aggravated allodynia in diabetic rats. Plasma NO level in the diabetic rats was significantly decreased compared with control rats. NO level in the CSF of diabetic rats did not differ from that of the control rats. NADPH-d positive cells were decreased in the DRG of diabetic rats. However, NADPH-d histochemistry in the diabetic spinal cord was not different from that of the control rats. Conclusions: Downregulation of NO expression in the diabetic rats may not be causally related to the development and/or maintenance of painful diabetic neuropathy.