We used the nitric oxide (NO) donor sodium nitroprusside (SNP) and the NO synthase inhibitor nitro-L-arginine methyl ester (L-NAME) to study the role of NO in the ischemic damage produced by occlusion of the rat middle cerebral artery (MCA). After MCA occlusion, intracarotid administration of SNP (2.5 mg kg h-2 for 1 h) enhanced the recovery of neocortical cerebral blood flow and of the EEG and reduced cortical infarct size by 76 +/- 2% (p < 0.01; n = 5). In contrast, administration of L-NAME (10 mg kg h-2) worsened the recovery of CBF and EEG and increased infarct size (+ 60 +/- 16%; p < 0.05; n = 5). The findings indicate that NO improves blood flow and reduces tissue damage after focal cerebral ischemia. Thus, NO donors could have an important role in the management of acute ischemic stroke.