Background: Streptococcus pneumoniae is a leading pathogen causing pneumonia, meningitis, otitis media, bacteremia and sinusitis resulting in significant morbidity and mortality. We examined in vitro activities of five quinolones in comparison with other antibiotics against 85 invasive pneumococcal isolates. Methods: Minimal inhibitory concentrations (MICs) of penicillin G, cefuroxime, azithromycin, clarithromycin, trimethoprim-sulfamethoxazole (SXT), ciprofloxacin, ofloxacin, levofloxacin, trovafloxacin and gemifloxacin were determined using a broth microdilution method. Results: The overall rates of resistance to penicillin (46%), cefuroxime (20%), azithromycin ( 20%), clarithromycin (18%) and SXT ( 46%) were considerable. Among all of the isolates, 9 isolates (11%) were highly resistant (MIC greater than or equal to2 mg/l) and 30 isolates (35%) had intermediate resistance (MIC 0.12-1.0 mg/l). Of the quinolones gemifloxacin and trovafloxacin had the highest activity. The penicillin resistance status of the isolates did not have any effect on the resistance pattern of new quinolones. Conclusion: The new quinolones show great potential in the treatment of invasive infections caused by both penicillin-susceptible and penicillin-resistant pneumococci. Copyright (C) 2004 S. Karger AG, Basel.