We analyzed the T cell receptor (TCR) V beta repertoire of lymphocytes obtained from patients with malignant effusion treated by locoregional immunotherapy. Polymerase chain reaction using a panel of V beta subfamily specific oligonucleotide primers(V beta 1-20) was employed after reverse transcription of mRNA isolated from the locoregional cells. No major oligoclonality of TCR repertoire was observed in effusion lymphocytes before the treatment. The expression level of V beta 13.1 repertoire was significantly higher in effusion lymphocytes than in peripheral blood lymphocytes before treatment. V beta 20 gene expression increased significantly after locoregional administration of OK-432. It is suggested that TCR V beta 13.1 may be responsible for effusion lymphocytes and TCR V beta 20 for OK-432-related antigenic stimulus.