The clinical and demographic characteristics of 86 Brazilian patients with clinically definite multiple sclerosis (MS) were compared to the cerebrospinal fluid (CSF) findings. The disease course was relapsing-remitting in 71% and chronic progressive in 29% of the cases. The IgG index was increased in 76% in the chronic progressive status and 46% and 49% during the bout and remission, respectively (p < 0.005). Only 36% of the MS patients using corticosteroids had increased IgG index, in comparison to the 64% of the patients without immunosupressive treatment. Oligoclonal IgG bands were detected in the CSF of 77% and 88% of the MS corticosteroids users and non-users, respectively. The quantitative study of intrathecal synthesis of IgG contributes to demonstrate the immunological differences between the two forms of MS, the relapsing-remitting and the chronic progressive. The treatment with corticosteroids decreases quantitatively the intrathecal synthesis of IgG but not the presence of oligoclonal bands.