In 28 adult patients with nonobstructive chronic bronchitis we investigated components of the immune system of the lower airways and the effects of treatment with Broncho-Vaxom (BV). An analysis of the washing from bronchoalveolar lavage (BAL) showed, in comparison with healthy controls, an elevation of total cell count (p = 0.003) as well as the IgA/albumin values (p = 0.02) and a reduction of the macrophage activity (p less than 0.001) in patients with chronic bronchitis. After BV a reduction in the total cell count (p = 0.05), an increase in the helper/suppressor T lymphocyte ratio (due mainly to the reduction in the suppressor cells; p = 0.04), a modulation of the IgA/albumin ratio, a stimulation of the impaired alveolar macrophage activity (p = 0.03) and increased concentrations of gamma-interferon (p = 0.03) were found in the BAL fluid of patients with chronic bronchitis. The salivary IgA/albumin ratio remained unchanged, the serum IgE concentration fell (p = 0.02) and the urinary IgA concentration rose (p = 0.002). Bronchial mucosa lesions, evaluated endoscopically in terms of structural damage, hyperemia and mucus production, were improved (p less than 0.01). These findings indicate that orally administered BV modulates disordered local and systemic immune functions in patients with chronic bronchitis.