A study was carried out in which aqueous solutions of acrylic acid-maleic acid copolymer (mole ratio of monomers: 3:2) were diluted with solutions of various salts [NaCl, MgCl2, CaCl2, SrCl2, ZnCl2, Al(NO3)(3) and Fe(NO3)(3)]. This copolymer was found to interact with all these salts to make solutions of enhanced acidity that infrared spectroscopy suggested was a result of charge stabilization of the polyanion by counterions occupying atmospheric or site-bound locations. The cations of the salts NaCl, MgCl2, CaCl2 and SrCl2 appeared to occupy atmospheric positions only; in contrast, with poly(acrylic acid) they showed some site binding. Zinc ions, on the other hand, gave identical bridging bidentate interactions with both polymers. The cations from the trivalent salts Al(NO3)(3) and Fe(NO3)(3) were atmospheric and site bound (bridging bidentate), respectively, and these were also different from their interactions with poly(acrylic acid). The addition of Fe(NO3)(3) to the copolymer caused gelation, as with poly(acrylic acid), but formation of the gel was slower and did not result in phase separation.