We examined the astrocytic GFAP and neuronal HSP-72 responses to transient middle cerebral artery (MCA) occlusion in the rat. Three groups of rats (n = 79) were studied: (1) fixed duration of MCA occlusion (120 min) and variable durations of reperfusion (0.5, 3, 6, 9, 12, 24, 48, 96 and 168 h); (2) variable durations of MCA occlusion (10, 20, 30, 60, 90, and 120 min) and a fixed duration of reperfusion (48 h); and (3) controls: sham operated rats and normal rats. Coronal sections from each brain were reacted with appropriate antibodies to GFAP and HSP-72 and stained with H&E for evaluation of cellular response to ischemia. Our data show that after MCA occlusion: (1) GFAP expression was found in the boundary zone to the infarct or in areas of selective incomplete ischemic necrosis; (2) GFAP expression was localized to the same areas where neurons express HSP-72 and are destined to survive the ischemic insult; and (3) HSP-72 expression was not found in astrocytes in any of the experimental groups. These studies suggest that after transient focal ischemia in the rat: areas where both GFAP and HSP-72 expression are lost are destined to become necrotic, even though cells may appear morphologically intact in the H&E preparations, and expression of GFAP and HSP-72 reflects astrocytic and neuronal viability, respectively.