To better characterize the cellular immune response taking place in the MS central nervous system, we investigated the blood and CSF T cell receptor (TCR) Vβ5 and Vb17 repertoire in HLA-typed patients with recently diagnosed MS or other neurological diseases (OND). Using a RT-PCR based technique, we analysed directly ex vivo the CDR3 size of TCR β chains utilizing Vβ5 (eight patients with MS and one with OND) or Vβ17 (eight patients with MS and six with OND) gene segments on paired blood-CSF samples. Globally, the analysis of Vβ5-Jβ and Vβ17-Jβ repertoire showed a less diverse pattern in the CSF samples than in the corresponding peripheral blood lymphocytes both in MS and in OND patients. However, we did not detect any recurrent clonal expansion within the Vb5⁺ T cells in MS patients, underlining the potential limits of Vβ5- based immunotherapy in MS. We found an expanded T cell population using the same Vβ17-Jβ1.6 combination with identical CDR3 length in the CSF of three MS patients and none of the control patients. These results suggest selective expansion of T cells expressing this segment gene in the MS central nervous system.