Hemorrhagic transformation after cerebral ischemia is a well known clinical concern. The frequency of intact basal lamina (BL), identified by laminin antigen, in hemorrhagic and nonhemorrhagic zones after middle cerebral artery occlusion (MCA:O) and 3-h MCA:O with reperfusion in adolescent male baboons was assessed. Parenchymal hemoglobin was not detected prior to 24-h reperfusion. A significant decrease in the density of laminin (BL) in hemorrhagic zones (6.2 +/- 2.4) compared with nonhemorrhagic ischemic zones (10.5 +/- 2.4) (p < 0.05) and nonischemic basal ganglia (17.0 +/- 2.7) (p < 0.01) was observed. Time-dependent changes in BL integrity appear linked to the extravasation of blood components.