Seven patients with supratentorial infarction were studied by means of serial nuclear magnetic resonance imaging using saturation recovery (SR) and proton density (PD) sequences. The earliest changes were visible in the more sensitive T1 dependent images (SR) and may reflect the cytotoxic component of ischemic brain edema. Further progress was also clearly discernible in the PD images and may mainly reflect the slower vasogenic component of ischemic brain edema. Nuclear magnetic resonance imaging seems to provide a new approach to early diagnosis of ischemic brain infarction. Furthermore, it may elucidate some aspects of the pathophysiology of ischemic stroke in man.