The serum level of glial fibrillary acidic protein (GFAp) has been recognised as predictor of neurological outcome after head trauma; elevated concentrations have also been measured after stroke, subarachnoid haemorrhage, and CA.6., 7., 8., 9., 10., 11., 12. GFAp is an intermediate-filament component of the astrocytic cytoskeleton highly specific to the central nervous system.13 Here, GFAP is linked to subarachnoid hemorrhage.