The in-vitro activity of cefpodoxime, the active component of the ester prodrug, cefpodoxime proxetil, was compared with that of other antibiotics. The susceptibility of bacterial isolates from patients with respiratory tract infections was determined by an agar dilution method. The MIC 90 s of cefpodozime for ampicillin-sensitive and β -lactamase-producing strains of Haemophilus influenzae were 0.12 and 0.25 mg/l, respectively; the MIC 90 s for ampicillin-resistant non- β -lactamase-producing strains was 1 mg/l. Time-kill curves of cefpodoxime against ampicillin-sensitive and ampicillin-resistant β -lactamase producing strains showed a time-dependent bactericidal activity. The MIC 90 s for ampicillin-sensitive and ampicillin-resistant Branhamella catarrhalis were 0.50 and 1 mg/l, respectively. The MIC 90 s for penicillin-sensitive pneumococci, β -haemolytic streptococci and Streptococcus agalactiae were 0.06, 0.06 and 0.12 mg/l, respectively. The inhibitory activity against penicillin-resistant pneumococci was limited; the MIC 90 was 4 mg/l.