The new fluoroquinolones clinafloxacin, CI-990 (PD 131112/PD 131628), sparfloxacin, and PD 138312 were bactericidal against Staphylococcus aureus with MICs > or = 4-fold lower than ciprofloxacin values. In a murine subcutaneous abscess model (subcutaneous/oral dosing) the new drugs displayed protective activities against five strains which were generally higher (up to 19-fold) than ciprofloxacin values.