Two animal models were used for the morphologic study of hypoxic or ischemic cerebral injury. In the first model ("Levine preparation") rats were subjected to a unilateral carotid artery ligation, followed by intermittent exposure to pure nitrogen. Damage, which was examined 24 h after this bypoxic insult, was largely restricted to the ipsilateral cerebral cortex. In the second model ("Pulsinelli preparation") severe bilateral transient ischemia was induced by permanent occlusion of both vertebral arteries, followed by temporary ligation of both carotid arteries. Damage was examined after short recirculation times and after a 3-day survival period. Injury was largely confined to the CA1 layer of the hippocampus. In both experimental models two types of cell change were prominent: coagulative cell change which was restricted to neurons, and edematous cell change which was largely confined to astrocytes. Studies on cerebral microcirculation revealed a close relationship between areas of reduced flow and areas with structural damage. Cytochemical demonstration of subcellular calcium indicated an early and important redistribution of this cation, indicative for toxic calcium overload in the cytosol. Data on therapeutic intervention with Ca2+-overload blocker flunarizine are included.