Antimicrobial activities of cefetamet (CEMT) against clinically isolated strains from patients with community acquired respiratory tract infections were investigated in comparison with those of other oral beta-lactam antibiotics during the period from January to March, 1998. The results are summarized as follows; 1. CEMT showed strong antimicrobial activities against three major pathogens causing community acquired respiratory tract infections, Streptococcus pyogenes, Streptococcus pneumoniae and Haemophilus influenzae. However, antimicrobial activities of CEMT against penicillins (PCs)-intermediate S. pneumoniae (PISP) and PCs-resistant S. pneumoniae (PRSP) were slightly weaker than those of some of the reference antibiotics. 2. No chronological changes of CEMT-MIC level were observed in the antimicrobial activities against S. pyogenes, H. influenzae, Moraxella subgenus Branhamella catarrhalis or Klebsiella pneumoniae subsp. pneumoniae. In contrast to this, due to the increase of PISP and PRSP strains, resistance to CEMT appears increasing with time.