Biophysical properties of pulmonary surfactant are best described by surface tension and surface viscosity. Beside lecithin, surfactant contains a variety of minor lipids, such as plasmalogens, polyunsaturated fatty acid containing phospholipids (PUFA-PL) and cholesterol. Plasmalogens and cholesterol improve surface properties of lipid mixtures significantly. A high content of PUFA-PL and plasmalogens in tracheal aspirate of preterm infants reduces the risk to develop chronic lung disease. Different preparations are available for exogenous surfactant substitution, however, little is known about lipid composition and surface viscosity. Thus, lipid composition and surface properties (measured with the oscillating-drop-surfactometer) of three different commercial surfactant preparations (Alveofact^R, Curosurf^R, Survanta^R) were compared. Lipid composition exhibited strong differences, SurvantaR had the highest proportion of disaturated PL and total neutral lipids, and the lowest proportion of PUFA-PL. Highest plasmalogen and PUFA-PL concentrations were found in Curosurf^R (3.8 ±0.1 vs. 26 ±1 mol%) when compared with Alveofact^R (0.9 ±0.3 vs. 11 ±1) and SurvantaR (1.5 ±0.2 vs. 6 ±1). In samples from Survanta^R viscosity increased above 18x10^-6 kg s^-1 at surface tension of 30 mN/m. Curosurf^R showed only a slight increase of surface viscosity below surface tensions of 25 mN/m and viscosity did not reach 5x10^-6 kg s^-1. By adding defined PL to Survanta^R a Curosurf^R-like lipid mixture (without plasmalogens) that exhibited biophysical properties like Curosurf^R was obtained. Different lipid compositions could explain some of the differences in surface viscosity. Therefore, PL-pattern and minor surfactant lipids are of importance for biophysical activity and should be considered when designing new synthetic surfactant preparations.