The activity of CI-934, a new carboxy-quinolone antibiotic, against gram-positive cocci and bacilli and gram-negative bacilli was compared with that of reference antibiotics. CI-934 demonstrated excellent activity against gram-positive organisms, including Corynebacterium sp. In addition, although the activity of CI-934 against gram-negative bacilli was less than that reported for similar agents, it was comparable to that of aminoglycosidic aminocyclitol antibiotics.