This study aimed at an analysis of glial fibrillary acidic protein (GFAP) in acute ischemic stroke, its association with the neurovascular status and its potential value as monitoring parameter. In 53 consecutive patients, serial venous blood samples were taken on admission, 6, 12, 18, 24, 48, 72, 96, and 120 h after stroke onset. The neurovascular status was assessed by repetitive extracranial and transcranial duplex sonography. Neurologic deficits were quantified by the National Institutes of Health stroke scale, and functional outcome was assessed with the modified Rankin Scale. Mean GFAP values were elevated from admission on with highest levels 48 h after stroke onset. GFAP release was highly correlated with severity of neurologic deficits and infarct volume. In patients with persistent middle cerebral artery occlusion, GFAP increased significantly compared with patients with normal sonographic findings (P = 0.019) and recanalization after thrombolysis resulted in a significant reduced increase (P = 0.038). GFAP concentrations were associated with the functional outcome after 3 months. Release kinetics of GFAP are associated with patients clinical deficits and infarct volume, depend on the neurovascular status on admission and on early recanalization after thrombolysis, and may be used as an additional predictor of the early course and functional outcome.