Monolayers of ethylcellulose, cellulose acetate, cellulose acetate-butyrate and lignin were spread on a Langmuir trough and their force against area curves determined. While the cellulose chains are extended, there is definite evidence for a folded structure for the lignin chains in the water surface. Films of these polymers were adjusted to an internal pressure of 2 mN m^–1 and the increases of pressure at constant area followed, after injection of solutions of (a) bovine plasma albumin and (b) epoxy resin. The resultant curves were convex to “amount injected” axis for (a) and concave for (b). It is suggested for (a) the polypeptide chains are unravelled and adsorb flat against the monolayer, while for (b) the epoxy chains adsorb by their terminal NH₂ groups and hang down as random coils vertically under the monolayer, the adsorbed chains exerting a lateral entropic repulsion on each other.