Ulifloxacin is a fluoroquinolone with potent antibacterial activity against a broad spectrum of Gram-positive and -negative bacteria. Ulifloxacin is the active form of the prodrug prulifloxacin and shows a highly potent antipseudomonal activity. Ulifloxacin is generally more active in vitro than other fluoroquinolones against a variety of clinical isolates of Gram-negative bacteria, including community and nosocomial isolates of Escherichia coli, Klebsiella spp., Proteus, Providencia and Morganella spp., Moraxella catarrhalis and Haemophilus spp. The activity of ulifloxacin against Pseudomonas aeruginosa varies between countries. Gram-positive organisms, including meticillin- or oxacillin-susceptible Staphylococcus aureus, Enterococcus spp. and Italian community isolates of Streptococcus pneumoniae are susceptible to ulifloxacin. Activity against Spanish strains of S. pneumoniae is moderate.