In order to evaluate antimicrobial activity of meropenem (MEPM), minimum inhibitory concentrations (MICs) of MEPM and control drugs were determined against clinical isolates in 1997. The results were as follows; 1. Antimicrobial activities of MEPM against Gram-positive bacteria were stronger than those of cephems (CEPs) and were approximately equal to those of imipenem (IPM) and panipenem (PAPM). 2. Carbapenems showed strong antimicrobial activities against Enterobacteriaceae, Glucose non-fermentative Gram-negative rods and Bacteroides fragilis group that were multiple drug resistant including the third generation CEPs. Antimicrobial activities of MEPM against these organisms were stronger than those of IPM and PAPM. By comparing antimicrobial activities of MEPM against Gram-negative bacteria in 1997 with those obtained in 1993, increase of resistance was not observed. 3. MIC-ranges of MEPM were low against the resistant strains of Pseudomonas aeruginosa to IPM and PAPM. It was considered that these resistant strains were not expressing oprD products (D2 porin protein), forming main outer membrane porin channels of carbapenems and basic amino acids.