In 1987, the most frequently identified pathogens in chronic respiratory tract infections in our clinic were Haemophilus influenzae, Pseudomonas aeruginosa, Branhamella catarrhalis, Streptococcus pneumoniae, Staphylococcus aureus and Klebsiella pneumoniae. Recurrent infection is a common phenomenon in patients with chronic respiratory tract infections, including chronic bronchitis, chronic bronchiolitis and bronchiectasis. H. influenzae is the most common pathogen in such patients. Macrolides, tetracyclines and new quinolones were effective to protect against recurrent infection of H. influenzae and these finding suggested that L-forms of H. influenzae may be significant in the recurrence of infection in patients with chronic respiratory tract infection. Bacterial colonization of the oropharynx is the initial event in most lower respiratory tract infections. Gargling protects against bacteria colonization of the oropharynx and occurrence of acute exacerbation.