Behcet's disease (BD) is a multisystem disorder with oral and genital ulcers, mucocutaneous, ocular, joint, vascular and central nervous system involvement. In this study, the peripheral T cell repertoire was analysed in patients with BD with MoAbs against T cell receptor (TCR) V beta gene products in CD4(+) and CD8(+) T cell compartments, and these were compared with rheumatoid arthritis (RA) patients and healthy controls (HC). In the CD4(+) T cell compartment, oligoclonal TCR V beta expression was observed in 56% of BD (10/18), 71% of RA (5/7) patients and 21% (3/14) of HC. In the CD8(+) T cell group 50% of BD (9/18), 57% of RA patients and 28% of HC (4/14) had an oligoclonal TCR repertoire. An increase of TCR V beta 5.1 subset was observed in five BD patients among CD8(+) T cells. Other elevations of TCR V beta subsets were heterogeneously distributed with one to three different V beta subsets. Our results suggest an antigen-driven oligoclonal increase of T cells in BD. There was no overall increase in any V beta group to suggest a superantigen effect. Analysis of the responsible antigens causing the increase in T cell subsets may give insights into the aetiopathogenesis of BD and immunomodulation of these T cells may lead to new treatments.