Imipenem/cilastatin sodium (IPM/CS) was administered to 55 patients with respiratory tract infections (RTI). A clinical evaluation of IPM/CS was carried out in 51 patients, 28 with pneumonia, 4 with pulmonary abscess, 1 with pyothorax, 6 with bronchitis, 9 with bronchiectasis, 1 with diffuse panbronchiolitis and 2 with RTI with chronic obstructive pulmonary disease, and the clinical efficacy rate was 78.4%. Causative organisms were isolated in 23 strains out of 20 patients, such as Staphylococcus aureus 4 strains, Staphylococcus epidermidis 1 strain, Streptococcus pneumoniae 1 strain, Branhamella catarrhalis 1 strain, Haemophilus influenzae 2 strains, Klebsiella pneumoniae 4 strains, Pseudomonas aeruginosa 6 strains, Pseudomonas sp. 1 strain, Acinetobacter calcoaceticus 1 strain, Acinetobacter sp. 1 strain and glucose non-fermentative Gram-negative rod 1 strain. An eradication rate of 70.6% was obtained. An overall eradication rate of main causative organisms in RTI including S. aureus, S. pneumoniae, H. influenzae and K. pneumoniae was 75.0%. Clinical adverse effects were observed in 5 patients, and these were eruption in 2, itching in 1, vomiting in 1 and drug fever in 1. Abnormalities in laboratory test results were observed in 8 patients. These disappeared or returned to normal values after completion or discontinuation of IPM/CS administration. IPM/CS appears to be a useful antibiotic for the treatment of RTI, especially severe infections.