The in vitro post-antibiotic effect (PAE) and batericidal activity of cefditoren was compared to that of cefixime, cefuroxime, loracarbef, cefaclor, amoxicillin, amoxicillin/clavulanate, clarithromycin, azithromycin, erythromycin, and ciprofloxacin against ATCC culture strains and clinical respiratory isolates. A PAE > 1 h was observed for cefditoren and generally for the macrolides against Streptococcus pneumoniae, beta-lactamase-negative Moraxella catarrhalis, and Streptococcus pyogenes, whereas the other beta-lactams showed mixed results. Cefditoren was the only beta-lactam showing significant bactericidal activity (>3 log reduction of viable cells) within 4 h against penicillin-resistant S. pneumoniae. Only cefditoren and ciprofloxacin showed significant bactericidal activity against beta-lactamase-negative (after 24 h) and beta-lactamase-positive strains of H. influenzae (after 12 h). Against beta-lactamase-positive strains of M. catarrhalis, cefditoren was the only agent to show significant bactericidal activity at 6 h (versus cefuroxime and ciprofloxacin at 12 h).