Streaming potential/current measurements for the characterization of charge formation processes at solid/liquid interfaces were combined with reflectometric interference spectroscopy. The simultaneous determination of electrosurface characteristics and the optical thickness of interfacial layers provides information on structural variations of adsorbed or covalently bound polymers and on charge dependent adsorption and desorption phenomena at solid/liquid interfaces. To demonstrate the potentialities of this extended approach for biointerfacial studies the authors report a series of experiments on the adsorption of the plasma protein fibrinogen at poly(octadecene-alt-maleic acid) thin films.