The Gibbs free energies of transfer of selected ions from water to concentrated aqueous ovalbumin and albumin (Delta(w ')(w)G(j)(o)) have been determined by ion-transfer voltammetry. Negative values for the tetrabutylammonium W, ion suggest its direct binding to ovalbumin. In contrast, for alkali cations and bromide, the Delta(w ')(w)G(j)(o) values are positive and increase with increasing ovalbumin concentration. Positive values are confirmed for concentrated aqueous albumin and poly (styrenesulfonate) as well. The largest value (ca. 10 kJ mol(-1)) is found for the transfer of K+ from water to 30 wt % ovalbumin. To reveal the solvation structure of these ions in ovalbumin solutions, X-ray absorption fine structure (XAFS) measurements have been performed at the K, Rb, and Br K-edges. Interestingly, the spectra obtained in 30 wt % ovalbumin solutions are identical to those for the corresponding hydrated ions. This strongly suggests that the first coordination shell structures of these ions are not affected by a large concentration of ovalbumin. The detected positive free energy of transfer is slightly lower than the hydrogen bonding energy of a water molecule and should thus come from the perturbation of the second and farther hydration shells of the ions under a water-shortage condition caused by a high concentration of ovalbumin.