We investigated the antibacterial activity of 12 antibiotics, including 4 carbapenems, against 200 strains of respiratory pathogens isolated in 1997, and compared the results with those obtained in 1993. The strains examined were 38 strains of methicillin-susceptible Staphylococcus aureus (MSSA), 32 strains of methicillin-resistant S. aureus (MRSA), 22 strains of penicillin-susceptible Streptococcus pneumoniae (PSSP), 10 strains of penicillin-resistant S. pneumoniae (PRSP), 53 strains of Pseudomonas aeruginosa, 19 strains of Moraxella catarrhalis, and 26 strains of Haemophilus influenzae. In 1993, 100 strains were examined. The minimal inhibitory concentration data of the present study showed that imipenem and panipenem were more active than the other agents against gram-positive bacteria, and that meropenem and biapenem were more active than the other agents against gram-negative bacteria. By comparing these results with those obtained in 1993, it was found that increase of resistance to carbapenem antibiotics was not observed against all the strains tested in this study. Thus, it can be stated that carbapenem antibiotics retain their position as the drug of first choice for severe infections.