To examine the antimicrobial activity of cefditoren (CDTR) against strains clinically isolated from outpatients at this hospital from November, 1993 to February, 1994, the minimum inhibitory concentrations (MICs) were determined including those of the control drugs. The results were as follows: 1. CDTR showed strong antimicrobial activities against Staphylococcus aureus subsp. aureus, Streptococcus pyogenes and Streptococcus pneumoniae. The MICs of CDTR against benzylpenicillin-insensitive or -resistant S. pneumoniae distributed in the lowest concentration range even compared to those of the control drugs. 2. CDTR showed strong antimicrobial activities against Haemophilus influenzae, Moraxella subgenus Branhamella catarrhalis, Escherichia coli, and Klebsiella spp. The MIC of CDTR against CEPs-resistant E. coli was lower than those of most control drugs. 3. Since the microbes described above the major pathogens for the community-acquired infections, CDTR will be effective against infectious diseases transmitted at outpatient visits.