A total of 480 recent clinical isolates were tested for their susceptibility to fleroxacin, norfloxacin, ofloxacin, gentamicin, piperacillin, cefoxitin, cefotaxime and imipenem. Fleroxacin showed potent activity against strains of Enterobacteriaceae, Acinetobacter spp. and gentamicin-sensitive Pseudomonas aeruginosa with MIC90s ranging from 0.06 to 2 mg/l, although the MIC90 for gentamicin-resistant P. aeruginosa strains was as high as 32 mg/l. The drug exhibited excellent activity against staphylococci, both methicillin-sensitive and -resistant. The overall activity of fleroxacin was comparable with that of norfloxacin and ofloxacin and higher than that exhibited by gentamicin and beta-lactam antibiotics tested.