To investigate clonality of local T cells in viral infections of the central nervous system, the T-cell receptor (TCR) repertoire was evaluated in T cells from the cerebrospinal fluid (CSF) of nine patients with mumps meningitis, using the polymerase chain reaction (PCR) assay. The usage of the variable region of TCR alpha chain gene (V alpha gene) in the CSF was widespread, and an average of 13 out of the 18 V alpha families were expressed. Quantitative PCR analyses showed that the V alpha gene expression was biased toward three or less V alpha families in the CSF of each patient. When compared with peripheral blood T cells, the average percentages of V alpha 11 and V alpha 12 gene expression were significantly higher in the CSF than in the peripheral blood. These results suggested that mumps-specific T lymphocytes with a restricted TCR repertoire are selectively recruited to the central nervous system in mumps meningitis, although polyclonal, probably nonspecific, T-cell populations are present in the CSF.