The aim of this study was to determine the prevalence and risk factors for lower airway bacterial colonization (LABC) in stable chronic bronchitis (CB). Forty-one outpatients with CB were enrolled in the study (age 63.8+/-9.1 yrs (mean+/-SD); forced expiratory volume in one second (FEV1)/forced vital capacity (FVC) 62.8+/-11.2; current/former smokers 24/17). All patients had normal chest radiographs and an indication for performing fibreoptic bronchoscopy (pulmonary nodule, remote haemoptysis). The protected specimen brush (PSB) was used for bacterial sampling, and concentrations > or = 1,000 colony-forming units (cfu) x mL(-1) were considered positive for LABC. The repeatability of the procedure in CB was assessed in a random subsample of 18 subjects. A 72.2% quantitative agreement was found in the repeatability assessment of the PSB technique. Positive PSB cultures, obtained in 9 out of 41 (22%) patients, mainly yielded Haemophilus influenzae. The logistic regression model, used to determine which variables were related to colonization, showed that LABC was associated with current smoking (odds ratio (OR) 9.83, confidence interval (CI) 1.16-83.20) and low FVC (OR 0.73, CI 0.65-0.81). Age and FEV1 were not related to LABC. It was concluded that the prevalence of LABC in stable CB is high (22%), and current smoking is an important risk factor.