The in situ adsorption/desorption studies of C-14-labeled human immunoglobulin G (IgG) were performed at the polyethylene (PE)/aqueous solution interface. The results reveal that the adsorbed protein molecules were predominantly packed in the end- on orientation. Desorption experiments showed that upon rinsing with buffer only minute fractions of adsorbed IgG could be removed from the PE surface. Both the competitive and the sequential adsorption measurements from the binary mixtures of hydrophobic IgG modified by attachment of 19 caprylic chains (19C(8)-IgG) and [C-14]IgG confirm that native IgG strongly adhered to the PE films. The specific recognition ability of adsorbed human IgG layers was studied by using specific (goat anti-human) IgG and nonspecific (goat anti-rabbit) IgG. It was shown that the prevailing effect of the interaction of [C-14]IgG adsorbed onto PE with the specific antibody was the increase in the surface radioactivity, which was attributed to the formation of a more densely packed layer of IgG molecules at the PE surface. It was also demonstrated that, whereas the specific antibody preadsorbed onto PE films retained the recognition ability relative to human IgG, its hydrophobic modification resulted in a substantial decrease in this ability.