The CSF proteins of 45 patients with inflammatory diseases of the CNS were studied in order to evaluate the information that the beta-globulin content may bring about the occurrence of involvement of brain tissue. The material was distributed in 6 groups according to the diagnosis of the cases: 10 patients had spinal cord and/or radicular inflammatory disease, associated or not with leptomeningeal involvement (group 1); 5 had acute leptomeningitis (group 2); in 5 the diagnosis of tuberculous meningo-encephalitis was made (group 3); in 10, of cysticercosis of the CNS (group 4); in 5, of neurosyphilis (group 5); in 10, of encephalitides (group 6). Total protein content was determined by the turbidimetric method of the trichloroacetic acid. The protein fractions were analyzed through paper strip electrophoresis. The results were evaluated in respect to normal values previously reported. The high gamma-globulin content of the CSF in inflammatory processes of the CNS hinders the evaluation of the changes occurring in the content of the other globulins; the interference of such factor is more marked when the inflammatory process is chronic. In such conditions the evaluation of the content of the other globulin fractions is better achieved by comparison with the albumin content, the values reported for each globulin being statistically compared to those obtained for the albumin fraction. By this procedure it was shown that in all 45 cases changes in the alpha-globulin content were not different from that found for the albumin fraction and it was concluded that these data bring no evidences indicating interference of other factors than those related to the blood-CSF barrier for the explanation of the changes in the alpha-globulins content of the samples studied. Significant differences were found in respect to beta and gamma globulins. The changes found in the gamma-globulin support the possibility that the increase of this globulin is conditioned by the local production. Data concerning to beta-globulin in the cases of groups 5 and 6 showed that the increases in the amount of this globulin were more marked than those observed for the albumin. This difference was statistically significant. It brings evidence of participation of a different factor in the explanation of the finding other than those accepted for the albumin fraction. The discussion on the nature of this factor supports the possibility of its relation to the changes in the protein metabolism of the brain, since the damage of the latter was present in the cases of these groups of patients. These data are in agreement to the findings on the changes registered in the content of this globulin in the CSF in degenerative diseases as it is reported in the literature. The changes in the beta-globulin content of the CSF which are more marked than those found in the albumin content bring useful information when the data are analyzed in respect to their respective normal values; they point out to the possibility of brain damage by the inflammatory process. In the basis of such evidence cases of the groups 3 and 4 are considered and it was found that the data obtained did not differ from those resulting from the surgical or necroscopic examination and from the follow-up of the patients.