The interaction of ciprofloxacin and ofloxacin with the bactericidal capability of human polymorphonuclear leukocytes against staphylococci was investigated. Exposure of Staphylococcus aureus and Staphylococcus epidermidis to subinhibitory concentrations of ciprofloxacin and ofloxacin did not significantly affect the uptake and killing by human polymorphonuclear leukocytes. In our assay, ciprofloxacin and ofloxacin in concentrations of one time the minimal inhibitory concentration induced a significant reduction in viable intraphagocytic S. aureus (percentages of survival: 43 and 51%, respectively) compared to the controls without antibiotic (percentage of survival: 65%). In contrast, both antimicrobials failed to produce a reduction in viable intraphagocytic S. epidermidis.