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Changes in plasma protein films preadsorbed and then exposed to plasma or deposited by plasma itself, onto various surfaces were studied using ellipsometry and other techniques to observe film thickness, antigenicity, and activity of adsorbates. Plasma deposited matter onto 7s gamma-globulins; if intact clotting factor XII was present in film or plasma, some removal followed from oxidized silicon substrate. Fibrinogen films were partially removed and, as did globulin to some extent, lost their antigenicity on exposure to intact plasma even if lacking factor XII. Antigenicity was maintained if the substrate had been non-wettable. Albumin was not adsorbed out of plasma though it competed well against purified proteins. Glass preexposed to proteins adsorbed factor XII out of plasma.At an air interface, water arranges itself like a hydrophobic film ( 1 ) ; even in very dry air, a metallic surface will obtain such a low energy coat of water (2, 3). Coiled protein molecules also adhere to relatively simple, non-yielding surface (4) to display complex surface properties. Onto a hydrophobic solid they adhere with hydrophilic residues exposed to the aqueous phase while on a hydrophilic one their apolar residues will be exposed (5). However, the forces involved in adhesion to a simple surface such as Lucite may be far from simple (6). On more complex surfaces such as gels and cell membranes (7) and in multilayer adsorption (8), reaction rates will be incomputable. If only 14 residue segments of any protein molecule are involved in adsorption (9), the distortion needed to accomplish such adhesion must have varied and indirect effects (10 11, 12, 13, 14) rendering the adhering shape sometimes more, rather than less, antigenic (15,16) or changing its enzymatic activity which is especially sensitive to orientation (17). Neither a hard 255

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