Down syndrome (DS) patients are frequently complicated with infections, autoimmune phenomena and hematological disorders, including transient abnormal myelopoiesis (TAM) in infancy and acute megakaryoblastic leukaemia (AMKL) in later life. In this study, serum levels of cytokines from 23 TAM and 15 AMKL patients were examined using the highly sensitive microsphere fluorescence system. Statistical differences between DS neonates with or without TAM were found in IL-1beta [median 7.0 pg/ml (0.34-271.6) verses 0.05 pg/ml (0.0-2.4), p=0.034], TNF-alpha [8.11 pg/ml (0.1-253.0) verses 0.41 pg/ml (0.1-1.5), p=0.041], and IFN-gamma [20.0 pg/ml (0.14-406.3) verses 1.5 pg/ml (0.14-5.79), p=0.036]. Moreover, abnormal inflammatory cytokinemia was also found in myelodysplastic syndrome (MDS) and AMKL with DS. These abnormal cytokinemia may have a role in the pathophysiology of TAM, MDS and AMKL in DS, especially in liver fibrosis or myelofibrosis.