Nitric oxide, a diffusible molecule which is constitutively expressed by neuronal isoform of nitric oxide synthase (nNOS) acts as an important non-conventional neurotransmitter in the nervous system. The distribution of nNOS-immunoreactive (-IR) and nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) positive neurons was studied by immunohistochemical and histochemical methods in upper lumbar (L1- L3) and lower lumbar and sacral (L4-S4) dorsal root ganglia (DRGs) and in relevant spinal cord segments after 15 min ischemia followed by 7 and 14 days of reperfusion. The intensity of nNOS-IR and NADPHd positivity was evaluated by densitometric analysis, using a software UTHSCSA Image Tool. A quantitative immunohistochemical and histochemical study have shown a strong vulnerability of nitrergic neurons in the spinal cord to transient ischemia and the following reperfusion periods. In addition, our results clearly show the increase of nNOS-IR/ NADPHd positivity in spinal ganglia laid outside the spinal cord. Distribution character of nNOS-IR/NADPHd positive fi bers coming out from DRGs refl ects the increase of nNOS-IR and NADPHd positivity in thin and thick myelinized axons of dorsal roots and dorsal funiculi. These results explain the participation of nitrergic system in nociceptive and proprioceptive circuits in the spinal cord. Supported by the APVV 0314 -06 and VEGA grants 2/0110/08 and 2/0015/08.