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The wetting properties of aqueous solutions of two therapeutic pulmonary surfactants (T PS) with respect to solid surfaces with different degree of hydrophobicity θw have been studied. A special procedure for hydrophobization of the SiO2-glass hydrophilic surface allows the preparation of hydrophobic solid surfaces with different θw. The contact angles of drops from a TPS solution onto SiO2-glass surfaces have been measured as a function of their θw. The completely hydrophilic SiO2-glass surface is essentially hydrophobized by the animal-derived TPS Curosurf as well as by the synthetic TPS CHF 5633. The hydrophobization depends on the surfactant concentration - the contact angles increase with increasing the Curosurf concentration C in the low concentration range, but they remain almost constant in a wide range of C > 90 μg/ml. Similar are the θ (θw) curves for aqueous solutions of both TPS. The thickness h of the wetting thin liquid fi lms from aqueous solutions of Curosurf as well as of CHF 5633 on SiO2-glass surfaces depends on θw of the solid surface. The h(θw) curves always pass a minimum. The h-values, as well as the h(θw) curve, are mainly determined by the balance of the positive (repulsive) steric and negative (attractive) hydrophobic disjoining pressures, which depend on the orientations and conformations of the molecules adsorbed on the wetting fi lm surfaces from the very complicated multi-component aqueous solutions. Practically no signifi cant difference in the wetting behaviour of the aqueous solutions of the natural TPS Curosurf and the synthetic TPS CHF 5633 has been established, however about 25% less Curosurf than CHF 5633 was needed to achieve almost the same wetting behaviour. [ABSTRACT FROM AUTHOR]