Na-23 NMR studies of counterion relaxation behavior in the presence of added electrolytes have been performed to determine the relative binding affinities of Na+, K+, Mg2+, and Ca2+ ions to the homopolymers of poly(sodium acrylate) (NaAA), poly(sodium 2-acrylamido-2-methylpropanesulfonate) (NaAMPS), and poly(sodium 3-acrylamido-3-methylbutanoate) (NaAMB). The addition of Mg2+ and Ca2+ to the biopolymer poly(sodium galacturonate) (NaGAL) was also investigated. Addition of salts yielded the order of binding Ca2+ > Mg2+ > K+ approximate to Na+ for NaAA and NaAMB and Ca2+ approximate to Mg2+ > K+ > Na+ for NaAMPS. Significant differences in the Na-23 NMR behavior for NaAA are observed for added Mg2+ and Ca2+ and were interpreted in terms of hydration of the polyelectrolyte near phase separation, although a conformational change cannot absolutely be ruled out. Differences observed upon addition of Mg2+ and Ca2+ in the NaGAL system are discussed in relation to the "egg-box" model of Ca2+ binding to NaGAL. Viscosity profiles for each of the polymers with the above cations are related to the NMR data Phase-separation studies on NaAMB demonstrate increased hydrophobicity of the polymer in the presence of excess Ca2+