The in vitro effects of ceftibuten on human polymorphonuclear leukocyte (PMN) chemotaxis, phagocytosis and chemiluminescence were investigated. PMN from healthy adult donors were incubated for 1 h in medium alone or in medium containing increasing concentrations of ceftibuten (4, 8 and 40 times the MIC for Escherichia coli). Up to 40 MIC ceftibuten did not significantly interfere with the function of PMN.