The adsorption of human serum albumin (HSA) and fibrinogen at n-butane plasma polymer surfaces prepared by low temperature plasma polymerization at different energy inputs have been investigated with in situ ellipsometry. Within experimental uncertainty, the adsorption of both fibrinogen and HSA is constant over the power range used for the preparation of the n-butane surfaces and corresponds to that found for other hydrophobic surfaces at similar conditions. Furthermore, novel copolymer surfaces of n-butane and nitrogen at different ratios were prepared and investigated. Increasing the nitrogen content in the gas mixture during deposition resulted in an increased density of interfacial amine groups, as evidenced by an increased wettability, an increased interfacial nitrogen content, and an increased surface positive charge. This, in turn, was found to result in an increased fibrinogen adsorption, but in a weak decrease in the HSA adsorption.