CFC-222 is a novel fluoroquinolone with potent and broad-spectrum antibacterial activity. The in-vitro and in-vivo activities of CFC-222 were compared with those of ciprofloxacin, ofloxacin, lomefloxacin and sparfloxacin. Against gram-positive bacteria such as Staphylococcus aureus (quinolone-susceptible and quinolone-resistant), Staphylococcus epidermidis, Streptococcus pneumoniae and Enterococcus faecalis, CFC-222 was more active than ciprofloxacin and similar to sparfloxacin. Against gram-negative bacteria, including Enterobacteriaceae, the in-vitro activity of CFC-222 was similar to that of sparfloxacin, but less than that of ciprofloxacin. However, it was less active than ciprofloxacin and sparfloxacin against Pseudomonas aeruginosa. In mouse systemic infection caused by S. aureus Smith or S. aureus TMS 33, CFC-222 demonstrated an activity similar to that of ciprofloxacin and sparfloxacin, but better than that of ofloxacin. The compound was more effective than ciprofloxacin and sparfloxacin in murine infection caused by Streptococcus pyogenes ATCC 8668. Against Escherichia coli, Klebsiella pneumoniae and Enterobacter cloacae infections, the efficacy of CFC-222 was similar to those of ciprofloxacin, ofloxacin and sparfloxacin. The activity of CFC-222 was similar to those of ciprofloxacin and sparfloxacin against P. aeruginosa MB4-16 in the same infection model. These results suggest that CFC-222 may be a promising therapeutic agent for the treatment of various bacterial infections.