Polypeptides can form a wide variety of aggregate states in solution depending on pH and salt concentrations. Repulsive electrostatic interactions as well as non-specific attractive interactions between polypeptides present serious challenges to discriminating aggregate states in solution. This poster discusses the use of batch light scattering methods to measure and quantify aggregates of a proprietary polypeptide as a function of ionic strength. Nonlinear regression methods can provide a good estimate of both interactions as well as aggregation equilibrium provided data of sufficient resolution are available.