In contrast to the healthy population, distal airway bacterial colonization may occur in patients with chronic lung diseases, who often have altered pulmonary defences. However, the information dealing with this issue is insufficient and is based mainly on nonspecific samples, such as sputum cultures. Using quantitative cultures of bronchoscopic protected specimen brush (PSB) and bronchoalveolar lavage (BAL) samples, we studied the bacterial colonization of distal airways in 16 healthy subjects, 33 patients with bronchogenic carcinoma, 18 with chronic obstructive pulmonary disease (COPD), 17 with bronchiectasis, and 32 with a long-term tracheostomy due to laryngeal carcinoma. All patients were without exacerbation, and free from antibiotic treatment at least 1 month before the study protocol. Thresholds for quantitative cultures to define colonization were > or = 10(2) colony-forming units (cfu) x mL(-1) for PSB and > or = 10(3) cfu x mL(-1) for BAL. Only one healthy subject was colonized by a potential pathogenic microorganism (PPM) (Staphylococcus aureus 4x10(2) cfu x mL(-1) in a PSB culture). Colonization was observed in 14 (42%) bronchogenic carcinoma patients (19 non-PPMs, and 10 PPMs); in 15 (83%) COPD patients (22 non-PPMs and 7 PPMs); in 15 (88%) bronchiectasis patients (20 non-PPMs and 13 PPMs); and in 15 (47%) long-term tracheostomy patients (5 non-PPMs and 13 PPMs). The two most frequent non-PPMs isolated in all groups studied were Streptococcus viridans and Neisseria spp. Haemophilus spp., Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis were the most frequent PPMs isolated in bronchogenic carcinoma, COPD, bronchiectasis and long-term tracheostomized patients, respectively. Pseudomonas aeruginosa colonization was infrequent in all the groups. Our results show that distal airway bacterial colonization is a frequent feature in stable patients with chronic lung diseases and also in patients with long-term tracheostomy. However, the pattern of colonization differs among groups studied. The knowledge of different colonization patterns may be important for future antibiotic prophylactic strategies and for the empirical antibiotic regimens when exacerbations occur in these patients.