Lomefloxacin is a promising new difluorinated quinolone with good antimicrobial activity and favorable pharmacokinetic properties. The in vitro activity of lomefloxacin was compared to other quinolones, expanded spectrum beta-lactams, and gentamicin. The lomefloxacin MIC90 against multiply resistant strains of P. aeruginosa was 4 mcg/ml, comparable to norfloxacin and ofloxacin. Lomefloxacin was also active against methicillin-resistant S. epidermidis and JK corynebacteria. The role of lomefloxacin in the treatment of infections caused by multiresistant organisms remains to be determined in clinical trials.