Isoelectrofocusing on polyacrilamide gel in the analysis of cerebrospinal fluid proteins is particularly suitable for investigations of gamma-globuline changes in the course of various neurological conditions. This technique makes it possible to recognise three patterns besides the normal one. The first is characterized by a diffuse increase in gamma-globulines with a great number of high density fractions showing uniform distribution in the alkaline pH area. It was observed in a case of Guillain-Barrè syndrome and in two cases of intramedullary tumours. It seems to be due to an alteration in the permeability of the blood-brain barrier. The second pattern shows a diffuse increase in the number of fractions and appears uneven owing to a certain amount of higher density bands which stand out clearly. This was observed in one case of tubercolous meningo-encephalytis, in one case of chickenpox encephalytis and one case of cryptococcal meningitis in a patient affected by lymphogranuloma. This pattern is probably due to an alteration of blood-brain as well as of immunological systems. The third pattern presents a clear fractionation of gamma-globulins gathered in a certain number of highly coloured bands, mainly in the most alkaline area of gel. This was observed in all the ten cases of multiple sclerosis and in the only case of subacute sclerosing panencephalitis. This may be attributed to the intrathecal production of oligoclonal gamma-globulines (Ig.G.).