Prulifloxacin, the prodrug of ulifloxacin (active component), is a newer fluoroquinolone with broad activity against enteric and nonenteric gram-negative bacilli. Ulifloxacin and other oral comparator agents were tested for activity against 582 gastroenteritis strains from global surveillance studies. Ulifloxacin was highly active against Escherichia coli, Salmonella spp., Shigella spp., Yersinia spp., Vibrio spp., Aeromonas spp., and Plesiomonas spp. (MIC(50)s and MIC(90)s, <or=0.03 microg/ml and <or=0.06 microg/ml, respectively). Only rare Aeromonas spp., Campylobacter spp., and E. coli displayed elevated MIC results (>or=4 microg/ml). Ciprofloxacin exhibited similar activity but was two- to fourfold less potent. Presently approved for clinical use in certain European countries and Japan, ulifloxacin was the most active of the antimicrobial agents tested against these gastroenteritis-causing pathogens.