Surface active material potentially present in the airway is difficult to analyse due to the tight binding of surfactant components to mucins. A surface active sol-fraction was obtained from sputum of patients with cystic fibrosis (CF), analysed and compared with the sol-fraction from sputum of tracheomized, non-CF patients. The release of phospholipids from CF sputum was relatively fast being completed within minutes, temperature dependent and averaged 5.6 +/- 2.2% of total phospholipid mass. In comparison to sputum, the phospholipid composition of the sol fraction was the same except for a lower percentage of phosphatidylethanolamine, which is usually found primarily cell membrane associated. The sol-fraction from the CF patient group had a lower percentage of phosphatidylcholine and about 3 times more surfactant protein A than that from the non-CF patients. Surface activity did not differ between CF and non-CF samples. Of interest, the adsorption rate (gamma ads, about 30-35 mN/m) and the minimal surface tension (gamma min, about 20-25 mN/m) were relatively low. These data support the hypothesis that surface active material can be released from sputum and that it might support its transport by reducing mucus adhesiveness to the airways.