The most important lower respiratory infection is pneumonia, the fourth leading cause of death. Most cases of bronchitis are of viral etiology and are not major problems. Empyema can present an important problem in management. Although the diagnosis of pneumonia is usually relatively straightforward, the specific etiologic diagnosis remains a major problem. Availability of empyema fluid or a positive blood culture result can be helpful in making the etiologic diagnosis, but these are unavailable in most patients. Screening of sputum Gram stains under 100 X magnification is very important; there should be fewer than 10 squamous epithelial cells, more than 25 polymorphonuclear leukocytes, or both per field of this size. The major causes of pneumonia are Streptococcus pneumoniae, Mycoplasma pneumoniae, anaerobic bacteria, Staphylococcus aureus, various gram-negative aerobic or facultative bacilli and Legionella. However, many other organisms are capable of causing pneumonia, even in the immunocompetent host. Further adding to the problem is the fact that a number of different organisms are manifesting increasing resistance to antimicrobial agents. Our study with ticarcillin plus clavulanic acid included seven patients with pneumonia, one with empyema, and one with purulent tracheobronchitis. Organisms recovered from pleural fluid, transtracheal aspiration and sputum or tracheostomy aspirate included multiple anaerobes, pneumococci, S. aureus, Hemophilus influenzae, Klebsiella pneumoniae, K. ozaenae, Pseudomonas aeruginosa, Acinetobacter, Enterobacter cloacae, Proteus mirabilis, beta-hemolytic streptococci, Neisseria meningitidis and Branhamella catarrhalis. Several of the organisms were ticarcillin resistant. Eight of the patients had cures and the other patient showed improvement. Only minor side-effects were encountered--Coombs' positivity (without hemolysis), eosinophilia, drug fever and one case of questionable neutropenia.