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Information on the structure of adsorbed monolayers of polypeptides is obtained from differential capacitance values measured in the presence of the adsorbing polypeptides and supporting electrolyte. The uncharged polylysine (pH>11) is strongly adsorbed and fails to desorb even from highly polarized mercury surfaces, thus no desorption peaks can be determined. The capacity values decrease with increasing polylysine concentration until a limiting saturation capacity curve is reached at a bulk concentration which decreases with the square root of the age of the mercury drop. The area per lysine residue on a saturated surface, calculated from the diffusion controlled adsorption kinetics, is 38Å2, irrespective of polarization. At lower pH values, when the charge on the polylysine increases gradually, a desorption peak appears at positive polarization, while at negative polarization a hump caused by reorientation of the polypeptide in the surface is observed. The surface confor‐mation reflects also the concentration of the polypeptide in the bulk. The area per lysine residue in the saturated surface layer adsorbed from very dilute solution at pH's 1.3–7 was calculated to be 22Å2. Polyglutamic acid (PGA) at low degrees of ionization (pH 4.6) produces a region of low capacities around the zero charge potential. It is desorbed from either a positively or a negatively charged mercury surface, giving rise to anodic and cathodic desorption peaks at +0.1 and −1.4 volts, respectively, relative to NCE. Completely ionized polyglutamic acid (pH 10.4) raises the differential capacity around the zero charge region and is expelled from the surface at higher negative polarization. The area per residue of fully ionized PGA was found from the adsorption kinetics to be 45Å2, corresponding to a spread out molecule with the residues in the trans position. At pH 4.6, when PGA is only about 20% ionized, the area per residue is 34Å2 at positively charged surfaces. This area decreases gradually with increasing negative polarization of the surface, to values between 13Å2 (40° C) and 18Å2 (0.9° C). These values are in accord with a helical conformation prevailing in the surface.

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