Although inflammatory changes are found throughout the airways of patients with chronic bronchitis, the mechanisms of the pathogenesis of chronic bronchitis are still unclear. The aim of this study was to investigate airways inflammation in patients with and without an exacerbation of bronchitis. Thirteen chronic bronchitic patients and nine normal subjects were studied. Eight of the patients were studied under baseline conditions (B), and five during an exacerbation of bronchitis (E). Bronchoscopy and bronchoalveolar lavage (BAL) with cytological analysis were performed, and the levels of granulocyte/macrophage colony-stimulating factor (GM-CSF) were determined in sera and in BAL supernatants by a solid phase enzyme immunoassay. Compared with patients under baseline conditions, chronic bronchitic patients with an exacerbation had increased numbers of BAL neutrophils (10+/-3 and 83+/-18x10(3) cells x mL(-1), respectively; p<0.0001) and of BAL eosinophils (1.9+/-0.5 and 6.7/-1.9x10(3) cells x mL(-1), respectively; p=0.014). Patients with chronic bronchitis, as a whole, had significantly increased levels of BAL GM-CSF compared to control subjects (36+/-5 and 19+/-4 pg x mL(-1), respectively; p=0.035), and similar levels of serum GM-CSF. Serum levels of GM-CSF were markedly increased in chronic bronchitic patients with an exacerbation, as compared with patients under baseline conditions (1.4+/-0.4 and 13+/-1 pg x mL(-1), respectively; p <0.0001). BAL levels of GM-CSF were also increased in chronic bronchitic patients with an exacerbation (25+/-5 and 54+/-8 pg x mL(-1), respectively; p=0.009). During exacerbations of chronic bronchitis there are changes in the cell populations in bronchoalveolar lavage of patients consistent with a recruitment of polymorphonuclear leucocytes in the airway lumen. The increased levels of granulocyte/macrophage colony-stimulating factor might suggest a role for this cytokine in the inflammatory processes of chronic bronchitis.