Aplastic anaemia (AA) is considered as an immune-mediated bone marrow failure syndrome. The mechanism is involved with a variety of immune molecules including interferon-c (IFN-c), tumour necrosis factor-a (TNF-a) and interleukins (ILs). IL-27 is a novel member of the IL-12 family, which mediates T cell response and enhances the production of IFN-c. However, little is known about the role of IL-27 in the development of AA. This study investigated the role of IL-27 and its receptor IL-27R in the pathogenesis of AA. Both the mRNA expression of IL-27/IL-27R subunits in the bone marrow mononuclear cells (BMMNCs) and the levels of IL-27 in the marrow plasma in AA were found to be higher than in controls. Increased IL-27 correlated with the disease severity of AA. Subsequently, we stimulated marrow T lymphocytes with recombinant human (rh)IL-27 and found that rhIL-27 enhanced the production of TNF-a and IFN-c in both CD4+ and CD8+ T lymphocytes from AA patients. We also detected increased TNF-a and IFN-c in the supernatants of BMMNCs from AA patients after IL-27 stimulation. In conclusion, our data suggest that elevated IL-27 and IL- 27-induced TNF-a and IFN-c overproduction might be involved in the pathogenesis of AA.