✓ Four enzymes have been investigated in spinal fluid and blood serum in two series of humans with varying degrees of brain injury. The values have been compared to those in a series of animals with standard experimental brain lesions. The enzymes studied showed high values, usually corresponding to the clinical severity of the injury, but not all figures are statistically significant. The highest values were found between the second and the ninth day following injury. The ultimate possibility of practical quantitative evaluation of brain injuries is discussed.