We tested the hypothesis that the composition of bronchial surfactant is normal in infants with cystic fibrosis (CF) in the absence of active lung disease but that it is altered by lower respiratory tract infection and inflammation. We examined the total phospholipid (PL), disaturated phospholipid (DSP), surfactant protein-A (SP-A), surfactant protein B (SP-B), and surface activity in bronchoalveolar lavage fluid from 27 subjects with CF whose mean age was 22.7 (SD 14.5) mo. Six infants with stridor served as non-CF controls. Twelve of the subjects with CF (CF-I group) had evidence of active pulmonary infection or inflammation which was absent in the remaining 15 subjects (CF-NI group). We found no differences in the surfactant composition or activity between controls and the CF-NI group. In contrast, the DSP/PL ratio was lower in the CF-I subjects than in both the CF-NI subjects (p = 0.05) and controls (p < 0.01) suggesting a disturbance of surfactant function. SP-A concentrations were higher in the CF-I group compared to the other two groups (p < 0.05). These results suggest that the bronchial surfactant of infants with CF is altered following lower airway infection and inflammation and is not a primary abnormality associated with this disorder.