Sulbactam/cefoperazone (SBT/CPZ), a new antibacterial drug, was administered to 14 cases with respiratory infections for a duration of 5 approximately 13 days at a daily dose of 4 g. Diagnoses of these patients were 7 respiratory tract infections, and 7 bronchopneumonias. The underlying diseases were chronic pulmonary emphysema in 6 cases, bronchial asthma in 2 cases, and one each of bronchiectasis, diffuse panbronchiolitis and lung cancer with bronchoesophageal fistula. All patients had underlying respiratory diseases and/or were more than 70 years old. The rate of clinical efficacy was 78.6%. The incidence of penicillinase production by isolated bacteria was 18.2% and that of cephalosporinase was 63.6%. SBT/CPZ was expected to be more effective than CPZ alone in 3 cases judging from the susceptibility of the bacterial strains concerned, to antibiotics. No side effects were observed. We conclude that SBT/CPZ is useful in the treatment of respiratory infections of patients of advanced age and/or with underlying respiratory diseases.