A parallelism can be found b,ween the CSF and the serums α 2- and γ-globulins; in such cases the proteins origin of both is the same. In other cases (subacute sclerosing leucoencephalitis, multiple sclerosis) the γ-globulins are probably produced inside the meningial envelopes. Moreover, in a series of cases (infectious meningitis, arteriosclerosis) it is difficult to find an univocal origin for the CSF proteins. The authors believe that some of CSF proteins may be produced, at least in part, inside the meningial envelopes. This could only be demonstrated with certainty under two conditions : first, by proving real qualitative differences between the CSF and serum proteins ; secondly, by revealing abnormal CSF proteins either in the nervous tissues themselves or in some of the CSF cells.