An adjuvant therapy to prolong the therapeutic window for stroke patients is urgently needed. This randomized, blinded, placebo-controlled study investigated adjuvant intravenous sodium nitrite with recombinant tissue plasminogen activator (rtPA) in middle cerebral artery occlusion (MCAO) with 6 and 2 h of ischemia followed by reperfusion in Sprague-Dawley rats (n=59). Quantitative diffusion, T(1)-, T(2)-weighted, and semiquantitative perfusion imaging were performed before and after reperfusion and at 48 h after ischemia to determine the spatiotemporal evolution of stroke. After 48 h animals were killed and examined to evaluate infarct size and evidence of hemorrhagic transformation. Factor VIII immunostaining was performed to assess vessel morphology. Nitrite treatment (6 h group: 37.5 micromol for more than 90 mins; 2 h group: 26.25 and 1.75 micromol for more than 60 mins) did not reduce infarct volume 48 h after MCAO compared with saline-treated placebo groups after 6 or 2 h of MCAO. Stroke progression from baseline to 48 h, based on the apparent diffusion coefficient and relative cerebral blood flow deficits before and after reperfusion and T(2)-weighted hyperintensity at 48 h, did not differ between treated and control animals. These results suggest that nitrite is not a protective adjuvant therapy to delayed rtPA administration after ischemic stroke in rats.