目的　观察选择性和非选择性一氧化氮合酶抑制剂在大鼠局灶性脑缺血时的作用 ,为临床应用提供实验依据。　方法　直接电凝大鼠大脑中动脉制成脑缺血模型 ,观察脑缺血后 30、6 0、12 0、180 min各时点及使用两种一氧化氮合酶抑制剂 (AG、L- NAME)后亚硝酸盐含量、测定缺血脑组织坏死体积并用电镜观察损伤海马 CA1区。　结果　脑梗塞体积测定及电镜显示 ,30 m in时 AG、L- NAME治疗组脑损伤程度重于缺血组 ,而 6 0～ 180 m in正相反。　结论　一氧化氮合酶抑制剂在大鼠局灶缺血性脑损伤后期呈现脑保护作用 ,选择性一氧化氮合酶抑制剂优于非选择性一氧化氮合酶抑制剂 ,脑缺血早期可考虑使用一氧化氮供体剂 Objective To observe the effect of selective and nonselective nitric oxide synthase inhibitors on focal cerebral ischemia in rats and provide experimental basis for clinical application. Methods The middle cerebral artery of rats were directly coagulated to establish the model of cerebral ischemia. After 30, 60, 120, 180 min of cerebral ischemia, the effects of two nitric oxide synthase inhibitors (AG, L- NAME), the necrotic volume of ischemic brain tissue was measured, and the hippocampal CA1 region was observed by electron microscope. Results The volume of infarction and electron microscopy showed that the brain injury in AG and L-NAME group was heavier than that in ischemia group at 30 m in, while the opposite was between 60 and 180 mins. Conclusions Nitric oxide synthase inhibitors exhibit neuroprotective effects in the late stage of focal ischemic brain injury in rats. Selective nitric oxide synthase inhibitors are superior to non-selective nitric oxide synthase inhibitors in early stage of cerebral ischemia Use of nitric oxide donors may be considered