The value of CSF enzyme estimations as indices of the extent of brain damage was studied in the experimental situation. Standard cold lesions of different severity were induced in cats. The activities of the enzymes CPK, HBDH, LDH, GOT, AND ChE were studied at half hour intervals in the cerebrospinal fluid (CSF). The ventricular and cisternal fluid pressure, and the arterial blood pressure were monitored continuously. Significantly higher enzyme levels were found in the animals with more severe injuries of the brain.