The cerebrospinal fluid (CSF) creatine kinase (CK) activity and isozymic spectrum (EC 220.127.116.11) have been examined in patients with craniocerebral injuries of varying severity. The CK activity has been elevated in all the patients. Three isoforms have been detected: CK-BB, CK-MB, and CK-MM. CK-BB has been detected in all the patients in the presence of the total CK activity; this is explained by the isozyme release from the brain tissue during the injury and as a result of functional and structural impairment of the cellular membranes in intensification of lipid peroxidation. The CK-MM activity is due to blood admixture in the CSF and to impaired hematoencephalic barrier during the injury. The presence of CK-MB in the CSF of patients without cardiac symptoms probably results from a recombination of CK-BB and CK-MM isoforms and is of no diagnostic significance. Measurements of the total and isozymic CK activity in the CSF of patients with craniocerebral injuries may become a test for the laboratory diagnosis of the trauma severity and course.