Little information is available on eosinophil activation and cytokine/chemokine responses in childhood asthma, thus we examined serum eosinophil cationic protein (ECP) and 27 types of cytokines/chemokines in acute exacerbation of asthma (acute asthma) and stable asthma. We determined peripheral eosinophil count, and the serum levels of ECP and 27 types of cytokines/chemokines (IL-1β, IL-1ra, IL-2,-4,-5,-6,-7,-8,-9,-10,-12,-13,-15 and-17, IFN-γ, IP-10, TNF-α, GM-CSF, G-CSF, MCP-1, MIP-1α and-1β, eotaxin, RANTES, PDGF-bb, FGF basic and VEGF) using a multiplex bead-based assay in 85 acute and 79 stable asthma patients, and 14 controls. We also examined the effects of systemic corticosteroids on these responses in acute asthma. The serum levels of ECP, IL-5,-6,-8 and-10, G-CSF, MCP-1, IL-1ra and IP-10 were significantly elevated in acute compared with stable asthma. Similarly, serum levels of ECP, IL-5 and IP-10 were significantly higher in acute asthma than in controls. Furthermore, in the acute phase, elevated serum levels of ECP, IL-5, IL-6, IL-1ra and IP-10, but not IL-8, IL-10, G-CSF and MCP-1 were significantly reduced after treatments that included systemic corticosteroids. Eosinophil activation could be induced by acute exacerbation of childhood asthma.