The novel 8-methoxyquinolone, moxifloxacin (Bay 12-8039), was compared with ciprofloxacin and eight other antimicrobials for activity against 425 strains Gram-positive clinical isolates, including 73 methicillin-resistant staphylococci, 35 vancomycin-resistant enterococci, and 80 penicillin- or eythromycin-resistant streptococci. Overall, 82% of the strains were inhibited at < or = 2 micrograms/mL. Moxifloxacin was more active than ciprofloxacin against staphylococci (8- to 32-fold), enterococci (0- to 16-fold), pneumococci (16-fold) and other streptococci (4- to 16-fold) when MIC90 results were compared. Moxifloxacin demonstrated good activity against all Gram-positive isolates tested except for ciprofloxacin-resistant enterococci (MIC90, 32 micrograms/mL) and methicillin-resistant staphylococci (MIC90, 8 micrograms/mL). Clinical trials should be initiated to define the role of this new quinolone.