OBJECTIVEDespite the significant recent progress in cerebral monitoring, it is still difficult to quantify the extent of primary brain injury and ongoing secondary damage after head injury. The objective of our study was to investigate S-100B protein as a serum marker of brain damage after severe head injury.METHODSEighty-four patients with severe head injury (Glasgow Coma Scale score ≤8) were included in this prospective study. Venous blood samples for S-100B protein were obtained as soon as possible after admission and every 24 hours thereafter, for a maximum of 10 consecutive days. Serum levels of S-100B protein were compared with outcome after 6 months, clinical variables, and the category of the Marshall classification of initial computed tomographic findings.RESULTSPatients who died had significantly higher serum S-100B values compared with those who survived (median, 2.7 &mgr;g/L versus 0.54 &mgr;g/L;P< 0.0001, Mann-WhitneyUtest). Nineteen (58%) of 33 patients who died had peak S-100B values of 2 &mgr;g/L or higher, compared with 4 (8%) of the 51 surviving patients (P< 0.0005, Fisher’s exact test). There was also a strong correlation between S-100B values and computed tomographic findings. Logistic regression analysis in a model with age, Glasgow Coma Scale score, intracranial pressure, and computed tomographic findings revealed S-100B as an independent predictor of outcome. Persistent elevation of S-100B levels for 2 to 6 days, even in patients with favorable outcome, may reflect ongoing secondary damage after severe head injury.CONCLUSIONS-100B may be a promising serum marker for assessing the extent of primary injury and the time course of secondary damage after severe head injury.