The chromatographic retention and wave characteristics of beta-lactoglobulins A and B were studied experimentally for various nonlinear chromatographic modes of operation, including isocratic and gradient elution and frontal and displacement chromatography. In contrast to typical Langmuirian behavior, beta-lactoglobulins A and B show increasing retention times with increasing column loading and diffuse fronts and sharp rears at moderate injection volumes. At higher injection volumes, the retention times increase initially and then drop. Significant tailing fronts are found in frontal chromatography, and the displacement effect is observed at high feed concentrations. The unusual behavior for both modes of overloaded chromatography has been explained consistently with an S-shaped isotherm model. The displacement chromatography of these non-Langmuirian adsorbates has also been analyzed. Serious tailing of displacement trains is observed, and, consequently, resolution is severely affected. The cause of non-Langmuirian behavior is postulated to be aggregation of adsorbed proteins on the stationary phase.