This study explores the neuroprotective action of tumor necrosis factor-alpha ( TNF-alpha) induced during physical exercise, which, consequently, reduces matrix metalloproteinase-9 ( MMP-9) activity and ameliorates blood-brain barrier ( BBB) dysfunction in association with extracellular signal-regulated kinase 1 and 2 ( ERK1/2) phosphorylation. Adult male Sprague -Dawleyrats were subjected to exercise on a treadmill for 3 weeks. A 2- h middle cerebral artery occlusion and reperfusion was administered to exercised and nonexercised animals to induce stroke. Exercised ischemic rats were subjected to TNF- a inhibition and ERK1/ 2 by TNF-alpha antibody or UO126. Nissl staining of coronal sections revealed the infarct volume. Evans blue extravasation and water content evaluated BBB function. Western blot was performed to analyze protein expression of TNF-alpha, ERK1/ 2, phosphorylated ERK1/ 2, the basal laminar protein collagen IV, and MMP- 9. The activity of MMP- 9 was determined by gelatin zymography. Tumor necrosis factor- a expression and ERK1/ 2 phosphorylation were upregulated during exercise. Infarct volume, brain edema, and Evans blue extravasation all significantly decreased in exercised ischemic rats. Collagen IV production increased in exercised rats and remained high after stroke, whereas MMP- 9 protein level and activity decreased. These results were negated and returned toward nonexercised values once TNF-alpha or ERK1/ 2 was blocked. We concluded that preischemic, exercise- induced TNF-alpha markedly decreases BBB dysfunction by using the ERK1/ 2 pathway.