In the mouse brain, focal necrotic lesion was induced by occlusion of the left middle cerebral artery. The volume of cerebral edema was quantified two days later by MRI in vivo. Histological examination after 2 to 3 months of survival revealed a loss of tissue in the affected brain hemisphere predominantly involving the cortex. The extent of brain atrophy as determined by morphometry correlated well with the volume of edema as measured by MRI. There was a cerebroprotective effect of the N-methyl-D-aspartate receptor antagonist MK 801 on the extent of brain damage as determined by both analytical methods.