Laboratory tests may be used to confirm the clinical differentiation of pseudoradicular syndromes and radicular syndromes. In the presence of pseudoradicular syndromes, CSF and blood samples yield no positive results with either non-specific or specific methods. Radicular syndromes give rise to positive findings; using non-specific methods they can be subdivided into inflammatory and non-inflammatory forms, with and without blood-nerve barrier impairment. Non-specific quantities of CSF routine diagnosis are total protein, albumin, leukocyte counts and differential cell count, L-lactate, intrathecal -IgG, -IgA, -IgM and immunoglobulin-class oligoclonal bands. Oligoclonal bands enable the highly sensitive differentiation of non-inflammatory from subacute-chronically inflammatory forms of radicular syndromes. Most of the specific quantities are the subject of current research, e.g. bacterial antigens, D-lactate, cultivation tests, polymerase chain reaction tests and pathogen-specific oligoclonal bands. Pathomechanisms affecting the permeability of the blood-nerve barrier to increasing concentrations of protein and to leukocyte subsets possibly explain the CSF findings in radicular and pseudoradicular syndromes.