CSF levels of beta2-microglobulin reflect immune activation and lymphoid cell turnover in CNS. There were proposed as a reliable marker of lymphoproliferative disorders in central nervous system in viral infections, inflammatory diseases, autoimmune diseases and malignancies. The aims of this study were to measure beta2-microglobulin on the automate Vidas of bioMérieux in 122 paired CSF and serum from control patients. We evaluated whether or not the elevated levels beta2-microglobulin in CSF can be a useful marker for diagnosis of lymphoproliferative disorders in 108 patients with neurological diseases. The concentrations of beta2-microglobulin in the CSF and sera from control patients were respectively 1.3 +/- 0.5 mg/L and 2 +/- 0.6 mg/L. The normal CSF to serum beta2-microglobulin ratio was 0.6 +/- 0.19. A CSF to serum beta2-microglobulin ratio greater than 1 was closely associated with intrathecal synthesis beta2-microglobulin in CNS lymphoproliferative disorders. Elevation of CSF beta2-microglobulin ratio is a sensitive marker of central nervous system disease activity by infiltrating lymphocytes in intracranial lymphomas (10/10) and paraneoplastic neurological syndromes (2/3).