The in vitro activity of nemonoxacin (TG-873870), a novel nonfluorinated quinolone, was tested against 2,440 clinical isolates. Nemonoxacin was at least fourfold more active than levofloxacin and moxifloxacin against most gram-positive cocci tested (shown by the following MIC(90)/range [microg/ml] values; community-associated methicillin [meticillin]-resistant Staphylococcus aureus, 0.5/0.015 to 2; Staphylococcus epidermidis, 0.5/0.015 to 4 for methicillin-susceptible staphylococci and 2/0.12 to 2 for methicillin-resistant staphylococci; Streptococcus pneumoniae, 0.015/< or = 0.008 to 0.25; Enterococcus faecalis, 1/0.03 to 128). Nemonoxacin activity against gram-negative bacilli was similar to levofloxacin and moxifloxacin (MIC(90)/range [microg/ml]; Escherichia coli, 32/< or = 0.015 to > or = 512; Klebsiella pneumoniae, 2/< or = 0.015 to 128; K. oxytoca, 0.5/0.06 to 1; Proteus mirabilis, 16/0.25 to > or = 512; Pseudomonas aeruginosa, 32/< or = 0.015 to > or = 512; Acinetobacter baumannii, 1/0.12 to 16).