The protein profile of the cerebrospinal fluid of 25 leprosy patients was studied. The results are compared to the serum protein profile, and correlated with the clinical progress of the disease, clinical form, and with the result of the Mitsuda reaction. The protein profile wal altered in 11 cases with raise of the albumin fraction in 6 cases, of γ-globulin in three cases, and of β-globulin in two cases. The relationship between the proportions of the cerebrospinal fluid and serum proteins was found to be altered. The relationship was increased regarding to albumin and β-globulin, and reduced regarding to α-globulin. The increase in the albumin fraction of the cerebrospinal fluid was observed in patients with undifferentiated forms of leprosy, and with greater frequency in cases of short evolution. The increase of the β-globulin fraction of the cerebrospinal fluid was observed in tuberculoid forms of the disease. Occurrence of an increase of this fraction and a positive Mitsuda test was observed, but statistical analysis of this showed no significant correlation. The increase of the γ-globulin fraction of the cerebrospinal fluid was found in cases of lepromatous leprosy, and may be secondary to the increase of this fraction in the serum. Occurrence of an increase of this fraction and of a negative Mitsuda test was found, and the statistical analysis of this showed a significant correlation.