Seven biological markers were studied in a population of 236 patients (144 females, 92 males) with multiple sclerosis as was the relation with the different degrees of diagnostic certainty (Rose and Poser scales), the time of evolution and number of bouts of the disease. The IgG concentrations, IgG ratio and the quantification of the intrathecal IgG synthesis by the Tourtellotte formula isolatedly constituted the most sensitive biological markers for the diagnosis of multiple sclerosis. Altogether, the determination of the number of cells, IgG and the IgG ratio achieved diagnostic sensitivity of 94% for defined multiple sclerosis. The IgG ratio was the most closely related biological marker related with the number of bouts and the time of evolution of the disease.