Lung surfactant is the surface active material of the lung alveoli that makes breathing possible. It consists of various amphiphilic components like phospholipids and surfactant proteins and can be isolated by bronchoalveolar lavage from the lungs. The function of the surfactant system of the lungs is dominated by the composition of the surface film. It is therefore highly probable that alterations of the lung surfactant in lung diseases are mostly reflected in the surface film of bronchoalveolar lavage fluid. The aim of the study was to investigate the possibility of isolating the native surface film of bronchoalveolar lavage (BAL) fluid with the high-performance surfactant purification apparatus HPS 1 from the technical as well as from the theoretical point of view. Basically this method represents a technique for the high-performance purification of ordinary surfactants to remove surface-active impurities and to achieve “surface-chemically” pure solutions. After adsorption from bulk BAL fluid (within 30 min) and subsequent compression of the adsorbed layer (by an surface area ratio of 1 to 30) the adsorbed layer was aspirated (one cycle) and the aspirated solution collected. This procedure was repeated for 100 and 200 times. The collected fractions of the aspirated solutions (after 100 and 200 cycles), the original BAL fluid pool and the residual bulk phase were analysed for the total protein, total phospholipids and phospholipid subclasses. In addition, the dynamic surface tension of the solutions was measured. Generally, there was an increase of the protein and the phospholipid concentrations in the aspirated fractions by a factor 2 to 3 in comparison to the corresponding concentrations of the BAL fluid. Analysis of the phospholipid subclasses shows that the aspirated solutions, i. e. the surface film, contains phosphatidylcholine, phosphatidylglycerol and phosphatidylinositol. Phosphatidylethanolamine was not detected in the surface film. The percentage of phoshatidylglycerol in the surface film (100 cycles) was noticeably increased by 11.4% and 7.0%, respectively, in comparison to that of the BAL fluid. The equilibrium surface tension values of the aspirated solutions amounted to 37.5 and/or 40.3 mN/m (lavage fluid 1) and 38.6 and/or 40.2 mN/m (lavage fluid 2). The results prove that proteins and different phospholipids are integral parts of the surface film of BAL fluid and that this technique provides a new advantageous possibility for the isolation of native lung surfactant.