The current status of the susceptibility of the main respiratory bacterial pathogens was evaluated by analysing the antibacterial activity of 21 drugs, including four carbapenems, against five species of the pathogens isolated between January 2005 and January 2006. A total of 157 strains were studied. Carbapenems inhibited the growth of all of the tested strains of Moraxella catarrhalis, Streptococcus pneumoniae and methicillin-susceptible Staphylococcus aureus strains at concentrations that were below the breakpoints set by the Japanese Society of Chemotherapy (2 and 1mug/mL for pneumonia and chronic respiratory tract infection, respectively). However, the majority of methicillin-resistant Staphylococcus aureus strains were resistant to carbapenems. Meropenem, but not the other carbapenems, inhibited the growth of all of the tested strains of Haemophilus influenzae isolates, including beta-lactamase-non-producing ampicillin-resistant strains, at concentrations of <or=1 microg/mL. The MIC(50) and MIC(90) of meropenem, 0.25 and 4 microg/mL, against Pseudomonas aeruginosa were the lowest of the carbapenems. By comparing these results with our previous data, it was found that there was no increase in resistance to carbapenems in any of the species tested. Thus, it can be stated that carbapenems have retained their position as key drugs for severe respiratory tract infections.