AIM To determine the effect of L-arginin e on cerebral blood perfusion following subarachnoid hemorrhage(SAH) in rats. METHODS Endovascular perforating SAH models were replicated in Wista r rats, and animals were divided into sham-operated group, SAH group and SAH+ L-arginine group. Dynamic changes of regional cerebral blood flow (rCBF) with in 24 hours were measured and serum nitric oxide(NO, NO - 2/NO - 3)levels at different time points within 24 hours were detected. Mean arterial blood pre ssure and blood gas were monitored during the experiment. RESULTS No obvious change in physiological parameters in the three groups was observed . rCBF and serum nitric oxide level at every time point after operation in SAH g roup were lower than those in sham-operated group. Pathological alterations abo ve in SAH+L-arginine group were less obvious than those in SAH group. CONCLUSION L-arginine, by antagonizing the decrease of nitric oxi de, exerts protective effect on secondary cerebral ischemia following SAH.