Infants with Down syndrome (DS) are at risk of developing a transient myeloproliferative disorder during the neonatal period, known as transient abnormal myelopoiesis (TAM). It is characterized by clonal myeloproliferation and is typically self-limiting. However, TAM can be a life-threatening disorder, when complicated by liver fibrosis. Here, we evaluated cytokine profiles in two male DS infants having TAM with or without liver dysfunction. The first patient, Patient 1, had hyperleukocytosis with cholestatic liver dysfunction, coagulopathy, and increased counts of blasts and was treated with exchange transfusion (ExT) due to the serious general condition. In Patient 1, serum interleukin (IL)-8 and plasma transforming growth factor (TGF)-β1 levels were markedly elevated before ExT (1,518.2 pg/mL and 17,635 pg/mL, respectively). After ExT, serum IL-8 and plasma TGF-β1 levels decreased to 40.7 pg/mL and 6,847 pg/mL, respectively. However, Patient 1 died on day 56 due to cholestatic liver dysfunction; namely, this patient represents fatal TAM. The second patient, Patient 2, had hyperleukocytosis with increased counts of blasts without liver dysfunction and was treated with cytarabine. In Patient 2, plasma TGF-β1 levels, but not plasma IL-8, were elevated (9,068 pg/mL and 28 pg/mL, respectively). Patient 2 was discharged on day 47. In summary, plasma TGF-β1 levels were elevated in the two DS infants with TAM, regardless of the presence or absence of hepatic fibrosis. Importantly, fatal TAM is assoicated with the elevated serum level of IL-8. We thus propose that IL-8 may be involved in the pathogenesis of liver fibrosis.