There is an increasing spread and incidence of penicillinresistant bacteria that are becoming less susceptible to commonly prescribed oral antimicrobials, including extended-spectrum cephalosporins. Against this background, we undertook this study to determine the prevalence of penicillin resistance in Streptococcus pneumoniae and the in-vitro activity of oral antimitrobials.Between April 1996 and December 1997, in 245 children with respiratory tract infections (bronchitis in 61, pharyngitis in 115, and tonsillitis in 69), 119 strains of Haemophilus influenzae, 89 strains of Streptococcus pyogenes, 61 strains of Streptococcus pneumoniae, 36 strains of Staphylococcus aureus, and 34 strains of Moraxella catarrhalis were isolated from the pharynx. The antimicrobial susceptibility of these isolates was assessed by a broth microdilution method. The isolation incidence of penicillinintermediately resistant S. pneumoniae (PISP) and penicillin-highly resistant S. pneumoniae (PRSP) was 59.0% and 13.1%, respectively. Most strains of PISP and PRSP were highly resistant to cefaclor, cefpodoxime, cefteram, cefdinir, clarithromycin, ampicillin, and minocycline, but susceptibile to ofloxacin and cefditoren (CDTR). The invitro activity of CDTR was superior to that of other cephalosporins, such as cefaclor, cefdinir, and cefpodoxime, when tested against both the β-lactamase-positive and -negative H. influenzae isolated. CDTR was also active against all the other strains, including methicillin-sensitive S. aureus, S. pyogenes, and M. catarrhalis. This study suggested that CDTR was a useful oral antibiotic for pediatric respiratory tract infections.