Abstract Nitrocellulose membranes were found to have a general negative electric charge in neutral and alkaline aqueous solutions, and to display a cation-exchange capacity of about 0.1 mequiv. NaOH/g. The adsorption of proteins seems to be caused mainly by (1) multiple electrostatic attraction between the numerous permanent dipoles (the protein molecule, (2) hydrogen bonds, (3) a general trend of the organized water molecules to force hydrophobic groups to the interface. However, in alkaline solutions those forces are either potentiated or weakened through ionic interactions between the negatively charged groups of the carrier and dissociated groups of the proteins. It was found that polyethylene glycol 6000 was firmly adsorbed to nitrocellulose in a way similar to polyoxyethylene sorbitan monoesters (the Tweens) and proteins. The relatively small adsorption of the above macromolecules on acetylcellulose membranes and on cellulose (contrasting with the high adsorption on nitrocellulose) was explained by the high dipole moment of the nitrate group as compared with that of the acetate and hydroxyl groups, and by steric factors influencing the accessibility of the dipoles.