Trovafloxacin (CP-99,219) was very active against Gram-negative species examined including Haemophilus influenzae, Moraxella catarrhalis, Legionella spp., Neisseria spp. and Escherichia coli (MIC90s < or = 0.03 mg/L). In general trovafloxacin was twice as active as ofloxacin but only half as active as ciprofloxacin against Gram-negative species. Trovafloxacin was active against Gram-positive organisms, including Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus pyogenes and Enterococcus faecalis (MIC90s < or = 0.25 mg/L). Against these organisms activity was eight to 16 times greater for trovafloxacin than for either ofloxacin or ciprofloxacin. In addition, Chlamydia spp., Mycoplasma spp. and Ureaplasma urealyticum were eight to 16 times more susceptible to trovafloxacin than to either ofloxacin or ciprofloxacin. These in-vitro data show that trovafloxacin is a broad-spectrum fluoroquinolone with greater activity against clinically important Gram-positive species compared with ofloxacin or ciprofloxacin.