Solution X‐ray scattering and osmotic pressure measurements were used to study protein interactions in concentrated solutions of either single species or mixtures of &agr;‐, &bgr;‐ and &ggr;‐crystallins from the eye lens. Different types of interactions were demonstrated in physiological conditions. &agr;‐ and &bgr;‐crystallins present repulsive interactions, well described by a repulsive coulombic electrostatic potential. The interactions between &ggr;‐crystallins are attractive. The overall repulsive interactions within the lens and account for its transparency. The interplay of repulsive and attractive interactions might account for the maintainance of a protein concentration gradient from the center to the periphery of the lens which improves the lens optical quality.