Objective-To investigate the predictive value of early serum levels of S100B and glial fibrillary acidic protein (GFAP) in traumatic brain injury. Methods-Sixty patients admitted within 24 h of trauma were included. Neurological status on admission (Glasgow Coma Scale), initial cranial computed tomography (CCT) studies (Marshall Computed Tomographic Classification), and outcome after 6 months (Glasgow Outcome Scale) were evaluated. S100B and GFAP levels were determined on admission and 24 h after trauma. Results-Blood levels of S100B and GFAP were elevated following head trauma and quantitatively reflected the severity of trauma. S100B levels after 24 h and on admission were of higher predictive value than CCT findings or clinical examination. GFAP, but not S100B levels rapidly declined after trauma. Conclusions-Blood levels of S100B and GFAP indicate the severity of brain damage and are correlated with neurological prognosis after trauma. Both methods can yield additional prognostic information if combined with clinical and CCT findings.