Study of cerebrospinal fluid (CSF) protein profile in 25 patients with subacute sclerosing leucoencephalitis (SSLE) was made. Twenty-one were also tested for serum protein profile. Six were tested for changes in CSF proteins at other stages of illness. In one, successive exams were done in CSF and serum prior to death. The results of this study confirmed those already recorded, that CSF hypergammaglobulin content was the principal alteration observed. This occured in all cases with the average majority distribution being between 30-50%, high being 60%. Study of serum protein profile showed less constant and less intensive alterations: increased alpha-2 globulin content in 14 cases and gamma globulin increases in 15 cases. The latter were slight in most of the cases. The serum/CSF gamma globulin relation showed increases in all of the cases, being more than 2.0 in 7 patients. The CSF beta/albumin index was calculed as proposed in a prior publication. In 20 cases its value was one or more. Such values suggest actual damage of central nervous system on the occasion of exam. Results were related to the time of illness. The CSF/serum gamma values were, on the average, more elevated in cases where disease was more advanced. The higher values of CSF beta/albumin index occured, in general, in cases in early stages of disease. Further considerations as to the usefulness of CSF beta/albumin index in evaluation of central nervous system lesions in the course of SSLE were also done based on cases where a second CSF protein profile was performed, as well as that which was submitted to successive exams prior to death.