Aplastic anaemia (AA) is thought to be an autoimmune-mediated disease with active destruction of haematopoietic cells through a T helper type 1 (Th1) cell response. Interleukin (IL)-17 is a potent proinflammatory cytokine produced by activated memory T cells. Recent studies indicate that IL-17 might be an essential effector cytokine in the T-cell mediated autoimmune process. It can drive the production of tumour necrosis factor-alpha (TNF-alpha), IL-1 beta, IL-6 and IL-8 by a variety of cells. The present study investigated the genetic and protein expression of IL-17 in patients with AA. The effect of IL-17 on IL-6 and IL-8 production by macrophages was also studied. AA patients showed an elevated expression of IL17A mRNA in bone marrow mononuclear cells and peripheral blood mononuclear cells. Higher IL-17 in bone marrow and peripheral blood plasma was also observed in AA patients compared with normal controls. IL-17 induced the production of IL-6 and IL-8 by macrophages both from patients with AA and normal controls. IL-17 stimulation also resulted in the production of TNF-alpha. These results suggested that elevated expression of IL-17 and IL-17-induced IL-6, IL-8 and TNF-alpha may be involved in the mechanisms of AA.