Beh double dagger et's disease (BD) is a multi-system inflammatory disorder, in which cytokine balance is polarized to Th1. In this study, the cell surface molecule expression, Th1/Th2, inflammatory cytokine levels in blood, and synovial fluid of CD3(+) T lymphocytes in BD were investigated. The study group consisted of 10 BD, 10 ankylosing spondylitis (AS) patients with peripheral arthritis, and 10 healthy subjects. Expression of cell surface molecules, intracellular IL-2, IL-5, IL-8, IL-10, IL-12, IFN-gamma, and TNF-alpha levels in CD3(+) T lymphocytes were determined by flow cytometry in synovial and peripheral blood mononuclear cells (PBMCs). Synovial and plasma cytokine levels were measured by ELISA and CBA. In PBMCs, CD4, CD25, HLA-DR expression and intracellular IL-12, and TNF-alpha levels of CD3(+) T lymphocytes were statistically increased in BD patients compared to healthy subjects. Compare to AS patients, CD25 and HLA-DR surface expression and intracellular IFN-gamma and TNF-alpha levels in T cells were significantly elevated in BD patients. In BD patients, there was an increase in IL-8 secretion; however, in AS patients, both Th1- and Th2-type cytokines were increased compare to healthy subjects. Intracellular cytokine expression did not show any difference in BD patients; however, IL-12 content of synovial fluid was significantly increased compared to AS patients. Our findings revealed that Th1 polarization occurred in both peripheral blood and synovial fluid of BD patients with arthritis. It is found no difference between synovial fluid analysis of BD and AS patients, showing the similarities in the pathogenesis of both diseases.