Chemokines play a major role in the recruitment of inflammatory cells during acute lung injury. Adult and newborn C57BL/6 mice were exposed to > 95% oxygen for up to 72 hours and 7 days, respectively. Chemokine mRNA abundance was evaluated in whole lung RNA by ribonuclease protection assay and in tissue sections by in situ hybridization. Monocyte chemoattractant protein (MCP)-1, macrophage inflammatory protein (MIP)-2, and interferon gamma-induced protein (IP)-10 mRNAs were present in whole newborn lung by 4 days of hyperoxia and were markedly elevated by 7 days. Levels of mRNA for MCP-1, MIP-1 alpha, and MIP-2 were elevated to a lesser extent by 72 hours of hyperoxia in adults. MCP-1 mRNA abundance was moderately elevated in scattered areas of perivascular tissue, peribronchiolar tissue, and the alveolar interstitium in 4-day hyperoxic newborns and markedly upregulated diffusely throughout the peripheral airspaces in 7-day hyperoxic newborns. MCP-1 mRNA abundance was limited to scattered perivascular areas and airspaces in 72-hour hyperoxic adults. These differences in the intensity, timing, and distribution of chemokine mRNA abundance between adult and newborn mice may help to explain the marked differences in their susceptibility to oxygen injury.