We investigated regulatory variants of five cytokine genes [tumour necrosis factor (TNF)-alpha, interferon (IFN)-gamma, transforming growth factor (TGF)-beta, interleukin (IL)-6 and IL-10] in 40 Italian patients affected by paroxysmal nocturnal haemoglobinuria (PNH) and aplastic anaemia (AA). Genotypes associated with high production of TGF-beta and IFN-gamma were more frequent in patients than in controls. Genetic regulation of the immunological pathways involved in the pathogenesis of bone marrow failure is suggested.