The minimum inhibitory concentrations (MICs) of tosufloxacin and other fluoroquinolone antimicrobials for Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella (Branhamella) catarrhalis, isolated, between January 2003 and July 2004, from patients suspected of having respiratory or otorhinological infections were determined. The results were compared with those for these organisms isolated in 1994, plus some H. influenzae strains isolated in 1998. Tosufloxacin was the most potent of all the antibiotics tested for antibacterial activity against S. pneumoniae (including penicillin-intermediate S. pneumoniae and penicillin-resistant S. pneumoniae). The MIC50 and MIC90 values did not differ from those obtained for the strains isolated in 1994. Fluoroquinolones exerted the most potent antibacterial activity against M. (B.) catarrhalis; the MICs for most of the strains were ≦0.06 μg/ml; fluoroquinolones inhibited the growth of all the strains at 0.25 μg/ml or less. Fluoroquinolones showed the most potent antibacterial activity against H. influenzae strains isolated between 2003 and 2004, and in 1994, but, for one H. influenzae strain isolated, between 2003 and 2004, the MICs of fluoroquinolones were high. Some strains of S. pneumoniae and H. influenzae were resistant to fluoroquinolones. Genetic analysis showed that all of these strains had mutations in the quinolone resistance-determining region, but there were no differences according to the years of isolation. These results indicate that tosufloxacin has potent antibacterial activity against major organisms isolated from patients with respiratory or otorhinological infections; further, the results of the present study did not differ from those obtained about 10 years ago.