In 47 patients with multiple sclerosis and 10 with other diseases of the nervous system determinations of haptoglobin were performed in the serum and cerebrospinal fluid by the method of Owen et al. The Hp level in the serum of multiple sclerosis patients was normal. Its level in the cerebrospinal fluid was higher in multiple sclerosis patients than in cases of other nervous system diseases (statistically significant difference, p less than 0.001). Raised value of the Hp/IgG index in the cerebrospinal fluid of multiple sclerosis patients points to increased permeability of the blood-brain barrier. The so called normal Hp/IgG index was found in multiple sclerosis patients with high Hp and IgG level. Low Hp/IgG index suggested the possibility of IgG synthesis in the brain of patients with this disease. The comparison of the protein level and protein indexes showed that raised IgG level in the cerebrospinal fluid was present in 80% of multiple sclerosis cases, raised Kabat index in 50%, and low Hp/IgG index in 48%.