Objective To investigate the distribution of nitric oxide synthase (NOS) in the spinal intermediate gray and it's relationship with hypertension. Methods Using NADPH\|d histochemistry method, the distribution of NOS in the spinal intermediate gray was investigated under microscope and analyzed quantitatively with image analysis system. Results 1 NOS positive neurons were observed mainly in the nucleus intermediolateralis thoracolumbalis pars principalis(ILp) and paracentral gray, as well as in the area of nucleus intercalatus spinalis. NOS positive cells existed in groups in ILp. The size and density of NOS positive cell groups differed with different spinal segments, no significant difference could be found in the distribution pattern of NOS positive neurons in the spinal intermediate gray between SHR and WKY. 2 The A value of NOS positive substance in the ILp of SHR was significantly lower than that in WKY. Conclusion The results imply that lower expression of NO in the area of ILp in SHR might be related to the development and maintenance of hypertension in SHR.\;