The solubility and hydration characteristics of κ-carrageenan-casein systems from bovine and caprine milk with incorporated salt (NaCl) were determined by means of sedimentation and 17O nuclear magnetic resonance (NMR) experiments. Relative salt interaction parameters for both caseins alone and caseins in mixtures with κ-carrageenan were assessed by nonlinear regression analysis from the characteristics of solubilization of the systems. The κ-carrageenan-casein interactions appear to depend largely on the ratios of κ- to αs1-casein and possibly αs2-casein. Second virial coefficients (B0 values) and hydration products derived from 17O NMR data suggest that while soluble at high salt, the caprine casein mixtures exhibit-strong interactions, whereas the bovine counterparts do not. At lower salt concentrations the solubility data and the 17O NMR data are in agreement. Thus, a structural dependence upon protein components in salt-containing κ-carrageenan-casein solutions from bovine and caprine milk has been demonstrated.