The adsorption of human serum albumin (HSA), IgG and fibrinogen at lipid surfaces was investigated with in situ ellipsometry. It was found that the adsorbed amount of these proteins at phosphatidylcholine (PC) and phosphatidylinositol (PI) surfaces was smaller than that at (hydrophilic) silica and (hydrophobic) methylated silica surfaces. PC and PI surfaces were quite similar with respect to the adsorption of these proteins. More precisely, the adsorption of HSA, IgG and fibrinogen at PC is lower than that at methylated silica roughly by a factor of 3, 15 and 100, respectively, corresponding to an adsorbed amount of 0.30 mg/m2, 0.20 mg/m2 and 0.05 mg/m2, respectively. The adsorption of lysozyme at PI was significantly larger than that of HSA, IgG and fibrinogen, but still smaller than that of lysozyme at silica and methylated silica. At phosphatidic acid (PA), the adsorption of all the proteins investigated was significantly larger than that at PC and PI. In fact, the adsorption at PA resembles that at silica and methylated silica more than that at PC and PI. These findings are correlated to previous results on the influence of the surface composition of colloidal drug carriers on their endocytosis.