In most cases of respiratory tract infection, antibiotic therapy has to be initiated before the results of microbiological examination are available. The four most common pathogens of acute exacerbations of chronic bronchitis are pneumococci, Haemophilus influenzae, Moraxella catarrhalis and Staphylococcus aureus. Pneumococci are the predominant pathogens of community-acquired pneumonia, followed by H. influenzae and staphylococci. Legionella, mycoplasma and chlamydia vary in frequency according to the population studied. Staphylococci, Pseudomonas, Enterobacter and Klebsiella spp. as well as H. influenzae are the major pathogens of secondary pneumonia. For reasons of cost and environmental problems, oral antibiotics ought to be used whenever possible considering the severity of the infection and patient circumstance. Parenteral antibiotics are indicated in severe infections in order to provide high therapeutic drug levels. Second generation cephalosporins are appropriate for initial therapy of lower respiratory tract infections. In case of severe infection, cephalosporins should be combined with an aminoglycoside, ureidopenicillin or quinolone. Cefuroxime has shown good clinical efficacy and tolerance in lower respiratory tract infections.