The MICs of LBM415, a new peptide diformylase inhibitor, were evaluated and ranged from 0.03 to 4.0 microg/ml for 300 pneumococci, irrespective of their beta-lactam, macrolide, and quinolone susceptibilities. By comparison, vancomycin, teicoplanin, linezolid, and quinupristin-dalfopristin were also active, with MICs </=2.0 microg/ml. Gatifloxacin and moxifloxacin were the most active quinolones tested, while the MICs of the beta-lactams rose with those of penicillin G. LBM415 at two times the MIC was bactericidal (99.9% killing) against six strains after 24 h.