Chlamydia trachomatis (Ct)-induced arthritis (CtIA) is characterized by persistent Ct infection, which stimulates secretion of cytokines in vitro. We therefore investigated whether CtIA patients have a unique cytokine profile in synovial fluid or serum in vivo. Because underlying Ct infection is overlooked in a high percentage of patients with initially diagnosed undifferentiated oligoarthritis (UOA), we examined whether determination of cytokines might also be of diagnostic relevance for this arthritis form. Matched serum and synovial fluid specimens from 26 patients with CtIA were analyzed and compared to those from 34 patients with UOA in whom Ct infection was excluded and those of nine patients with rheumatoid arthritis (RA). In 15 CtIA patients, Ct DNA from synovial fluid could be amplified by polymerase chain reaction. The following cytokine or cytokine antagonists were measured by enzyme-linked immunosorbent assay: interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha, IL-6, IL-1 receptor antagonist, and soluble TNF receptor p75. No statistically significant differences in cytokine levels between patients with CtIA or the other arthritis forms were detected. Also, comparison between CtIA patients with (n = 17) and without Chlamydia DNA (n = 9) in synovial fluid revealed no significant differences for these cytokines. Cytokine levels in serum and synovial fluid were not different between CtIA, UOA without Ct infection, and RA patients. The intracellular presence of Ct was not associated with a specific profile of these cytokines in vivo.