Gamma globulin was determined by precipitation of the protein in a 2-5 cc sample of cerebrospinal fluid with a zinc sulfate solution in barbital buffer at a pH of 7.3. The precipitate was washed, and determined photometrically with the phenol reagent of Folin and Ciolcalteau, measurements being made at a wavelength of 660 m[mu]. Spinal fluids from 200 patients with various diseases were examined, both for gamma globulin and total proteins. Values for gamma globulin which exceeded 13% of total protein were considered elevated. Twenty-two of 30 patients with multiple sclerosis showed elevated values. Other conditions giving markedly elevated gamma globulin values were central nervous system syphilis and hyperglobulinemia from various causes such as multiple myeloma, Boeck''s Sarcoid and hepatic cirrhosis. Some patients with elevated cerebrospinal fluid protein values, or with blood in the spinal fluid gave borderline gamma globulin values of 13-15% of total protein. In 2 patients with multiple sclerosis a difference in gamma globulin on repeated spinal punctures suggested a fluctuation with the course of the disease.