SUMMARYThe unstimulated and induced production of granulocyte-macrophage colony-stimulating factor (GM-CSF), granulocyte colony-stimulating factor (G-CSF), IL-3, IL-6, stem cell factor (SCF), IL-1b, tumour necrosis factor-alpha (TNF-a), TNF-b, interferon-gamma (IFN-g) and transforming growth factor-beta (TGF-b) was determined after culture of blood mononuclear cells from 22 patients with severe b-thalassaemia in a regular transfusion programme, five non-regularly transfused patients with b-thalassaemia intermedia and nine normal persons. A distinct pattern of cytokine production in thalassaemic patients was detected, namely a low unstimulated production of all cytokines and a significant increase in the stimulated production of IFN-g, TNF-a and IL-1b; these abnormalities were more pronounced in the more heavily transfused older patients. The increased production of the above cytokines, which usually characterize the acute response to infectious agents and have a negative effect on erythropoiesis, may explain the deterioration of anaemia found in thalassaemic patients during acute infections.