A chromatographic method is used to measure lysozyme-lysozyme interactions in aqueous salt solutions as a function of solution conditions (pH, ionic strength, and salt type). Compared to static light scattering and membrane osmometry, the chromatographic method requires significantly less protein. To interpret retention-time data, it is necessary to account for multibody interactions between a mobile lysozyme molecule and immobilized lysozyme molecules on the support surface. The interaction between lysozyme molecules may be described by a potential of mean force that contains hard-sphere, electrostatic, and square-well contributions. Square-well depths from chromatographic data are in semiquantitative agreement with those from osmotic second virial coefficients from static light scattering measurements.