The brain-type isoenzyme of creatine kinase was determined in serum (S) and cerebrospinal fluid (CSF) in 37 patients with severe head injury, and a correlation was made with the Glasgow coma score and Glasgow outcome score. All patients with normal S-CKBB and CSF-CKBB activities had a coma score of 15, i.e., no neurological deficits, at six hours after the trauma and a good outcome. All 15 patients with a significant increase in the enzyme in serum and CSF had a coma score less than 15. The outcome was still good for five of these patients, while six were moderately disabled, two were severely disabled, and two died. There was no correlation between the individual CKBB-values and the outcome.