Multiple sclerosis (MS) is often characterized by a intrathecal synthesis of immunoglobulins (Ig) in cerebrospinal fluid (CSF), which may be evaluated in several ways: ratio methods (IgG index, Schuller's or Tourtelotte's formulae) or demonstration of an oligoclonal distribution, or both. In a retrospective study, 256 CSF analyses were evaluated. The 4 parameters studied were disturbed in about the same proportions in each of the 3 MS subgroups of Mac Alpine's classification. An oligoclonal distribution is more rarely present in pathologies other than MS. None of these tests is specific for the diagnosis of MS. Haptoglobin index variations do not distinguish between the different groups of patients. From a physiopathological point of view, however, they may perhaps reveal an acute local inflammatory reaction, different from the immune reaction giving rise to the Ig synthesis.