OBJECTIVES: To determine whether the spontaneous production of interleukin 6 (IL-6), oncostatin M (OSM), soluble IL-6 receptor (sIL-6R) and soluble gp130 (sgp130) from peripheral blood mononuclear cells (PBMC) is increased in patients with systemic sclerosis (SSc). METHODS: The culture supernatants of PBMC from patients with SSc (n = 33) and healthy controls (n = 20) were examined by enzyme-linked immunosorbent assay. RESULTS: The production levels of IL-6, OSM and sIL-6R were significantly higher in patients with SSc than in controls. However, sgp130 levels in supernatants from patients with SSc were not significantly elevated when compared with those from controls. Soluble IL-6R levels correlated significantly with the severity of pulmonary fibrosis in patients with SSc. CONCLUSIONS: The enhanced production of IL-6, OSM and sIL-6R from PBMC may cooperatively contribute to the disease process in SSc. In particular, enhanced sIL-6R production from PBMC may be related to the development of pulmonary fibrosis via enhancement of IL-6 signal transduction in SSc, since sIL-6R can act as an agonist of IL-6.