The principal aim of this study was to evaluate the in-vitro activity of new quinolones against clinical strains of Streptococcus pneumoniae. Four hundred and fifty-two single clinical isolates (of which 362 were susceptible to penicillin, 54 intermediate and 36 highly resistant) were tested against penicillin, cefuroxime, ciprofloxacin, levofloxacin, trovafloxacin and Bay 12-8039. Of the tested S. pneumoniae strains, 97.1 % had MICs of trovafloxacin of < or = 0.25 mg/L, and 96.7% had MICs of Bay 12-8039 of < or = 0.25 mg/L (difference not statistically significant); 81.9% of strains had MICs of cefuroxime of < or = 0.25 mg/L (P < or = 0.001 against both quinolones). Only 4% and 0.7% of the strains had MICs of levofloxacin and ciprofloxacin respectively of < or = 0.25 mg/L. Compared with older quinolones, trovafloxacin and Bay 12-8039 have good in-vitro activity against S. pneumoniae.