1H MRI permits detection of edema in the brain. In a middle cerebral artery stroke model in the cat, we found a significant correlation between an edema index based on MRI and a sensitive metabolic index of ischemia, the in vivo oxidation status of mitochondrial cytochrome aa3 determined by near-infrared reflectance spectrophotometry (r = -0.70, alpha = 0.001). This result suggests that a simple, noninvasive study using MRI can provide an index of the extent of ischemic damage in an experimental acute stroke model.