The frequencies of pathological results in 143 CSF samples of MS patients from the years 1964–1967, and 206 samples from 1968–1973 were compared after agar electrophoresis and cytological differentiation. As they were in good agreement, the two series were combined into one group of 349 MS patients for further comparison with three groups with other neurological diseases (inflammatory, neoplastic and vascular brain affections). Although the absolute γ-globulin values (mg/l) are somewhat more frequently pathological than the relative values (rel%), they also correlate significantly with total protein and, therefore, do not offer a criterion with a diagnostic value of its own. From them - as from the total protein – a pathological CSF state can be concluded, but no discrimination between MS and other diseases of the central nervous system is possible. The relative percent values for the γ-globulins are much less correlated with total protein in all the 4 groups compared; consequently, they represent a more specific criterion for differential diagnosis. Compared with MS the frequency of an increased relative GG content is about the same in other inflammatory diseases of the CNS, but decreases by a factor of 3 in brain tumors and by a factor of 6 in vascular affections of the CNS. In order to distinguish between MS and other brain diseases the relative GG values together with the total protein and the observation of oligoclonal zonation of the γ-globulin region are therefore most valuable diagno