The main objectives of this study were to investigate the dynamics of the inflammatory and anti-inflammatory responses in febrile neutropenic children, throughout the progression of intercurrent sepsis and recovery of leukocytes, by means of the measurement of circulating cytokines (IL-1β, TNF-α, IL-10, IL-12/23p40, IL-21, IL-6, IL-8, IL-17, G-CSF, and GM-CSF) in plasma. The gene discussed is IL21; the disease is Sepsis.