Eighty-two episodes (77 cases) in which any pathogens were isolated from transtracheal aspiration (TTA) and which satisfied the new clinical criteria of acute bacterial bronchitis were clinically evaluated. Major pathogens isolated from TTA included H. influenzae, S. pneumoniae and B. catarrhalis. Fever developed in 91.5% of the patients. Sputum volume averaged 16.3 +/- 14.9 ml per day. All the patients suffered from coughs, which were so severe as to disturb sleep in 8.5% of the patients. Inflammatory indices included WBC 9738.0 +/- 3158.5/microliter, CRP 10.1 +/- 7.9 mg/dl and ESR 69.0 +/- 38.8 mm/hr on average, PaO2 fell in most cases. Compared to the group of patients with acute bacterial bronchitis from which a single pathogen was isolated, the numbers of elderly patients and smokers were significantly more in the group of multiple pathogens isolated from TTA. Prior episodes related to the development of acute bacterial bronchitis were upper respiratory inflammation in 46.3% and undergoing bronchoscopy in 4.9% of the patients. Antibiotics therapy cured acute bacterial bronchitis in 96.3% of the patients. In spite of treatment, 3 patients developed pneumonia and died.