A new method has been developed in which a reversibly adsorbed layer of a surfactant (sodium dodecyl sulfate, SDS) is covalently immobilized in one step onto a hydrophobic substrate (poly(propylene), PP) by applying an argon plasma treatment. The adsorption of SDS from aqueous solutions onto PP surfaces was studied with X-ray photoelectron spectroscopy (XPS). Plateau levels of adsorbed SDS were reached within 10 s using SDS solution concentrations above the critical micelle concentration (CMC). At SDS concentrations below the CMC almost no adsorption took place, whereas at SDS concentrations above the CMC constant adsorption levels were measured. Preadsorbed SDS layers could be completely desorbed after immersion of the SDS-coated substrates in water for 90 min. If PP surfaces with preadsorbed SDS were dried and plasma-treated with an argon glow discharge and then immersed in water for 90 min, intact sulfate groups were present at the surface as shown by ion exchange and XPS measurements. This indicates that SDS preadsorbed onto PP surfaces can be immobilized by a plasma treatment. It is concluded that plasma techniques can be used to immobilize physically adsorbed surface active compounds onto substrates. This is a useful way to derivatize inert substrates with various polar or nonpolar groups.