OBJECTIVE Impaired neutrophil (PMN) function, due in part to release of immature PMNs into the circulation, contributes to the increased rate of infection observed in adults suffering blunt trauma. The objective of this study was to determine whether similar events occur in children. METHODS We assessed PMN chemotaxis and PMN maturation in 25 children (7 young children and 18 adolescents) and 25 adults 1 to 9 days after suffering blunt trauma, and in healthy adult control subjects. PMN chemotaxis was determined using a standard micropore filter assay, whereas PMN maturation was determined with 31D8, a novel monoclonal antibody that binds to mature PMNs more avidly than immature PMNs and band forms. RESULTS In patients suffering blunt trauma, mean PMN chemotactic values were similar among children (44.6 +/- 2.3 microns) and adults (41.3 +/- 2.1 microns) and both were significantly less than among healthy adults (53.5 +/- 2.4 microns, P < .0005). PMN chemotactic values increased significantly in the 9 days after trauma for both children and adults (F = 13.8, df = 1, P < .0002). Mean PMN 31D8 binding among children with trauma (92.5 +/- 5.2) was significantly less than among healthy adults (117.6 +/- 5.4, P < .0009). CONCLUSIONS Impairment in PMN chemotaxis occurs in children after blunt trauma and is due in part to release of immature PMNs into the circulation.