In order to evaluate the antimicrobial activity of meropenem (MEPM), minimum inhibitory concentrations (MICs) of MEPM and control drugs were determined against clinical isolates from blood and cerebrospinal fluid that were obtained from January, 1993 to December, 1994. The results are summarized as follows; 1. The MIC-range, 50% MIC (MIC50) and 90% MIC (MIC90) of MEPM were equal to those of imipenem (IPM) and panipenem (PAPM) against Streptococcus pneumoniae including benzylpenicillin (PCG)-insensitive or -resistant S. pneumoniae, Streptococcus agalactiae and Listeria monocytogenes which are Gram-positive strains, and were stronger than those of ampicillin (ABPC) and cefotaxime (CTX). 2. The MIC-range, MIC50 and MIC90 of these 3 drugs of carbapenems (MEPM, IPM and PAPM) were different against Escherichia coli and Haemophilus influenzae which are Gram-negative strains. The MIC90 of MEPM was < or = 0.025 microgram/ml and those of IPM and PAPM were 0.2 microgram/ml against E. coli. The MIC90 of MEPM was 0.1 microgram/ml, that of IPM was 25 micrograms/ml and that of PAPM was 6.25 micrograms/ml against H. influenzae. Thus, the antimicrobial activity of MEPM was stronger than those of IPM and PAPM. The MIC90's of IPM and PAPM against H. influenzae were high with the MIC of IPM at 12.5 approximately 25 micrograms/ml and the MIC of PAPM at 3.13 approximately 12.5 micrograms/ml against 3 IPM-resistant strains among 17 isolates. 3. The MIC90 of ABPC was 0.39 microgram/ml and that of CTX was 0.1 microgram/ml against 20 strains of S. pneumoniae including 6 strains of PCG-insensitive or resistant S. pneumoniae. The MIC90 of ABPC and CTX were higher than those of 3 carbapenem drugs. There were E. coli of 8 strains with ABPC-high resistance (the MIC of ABPC was > 100 micrograms/ml) and 2 strains for which MIC of CTX were 0.39 microgram/ml and 3.13 micrograms/ml. It was found that 29.4% of H. influenzae were beta-lactamase producing strains. 4. It appeared that antimicrobial activities of carbapenems, particularly MEPM were strong against clinical isolates from blood and cerebrospinal fluid. MEPM will be first choice drug by empiric therapy in infections including sepsis and purulent meningitis.