The Calypso automated protein association and aggregation system from Wyatt Technology Corp. includes hardware and software for composition-gradient multiangle light-scattering measurements. Enabling nondestructive, quantitative characterization of protein-protein interactions and aggregation kinetics in native solution, the system does not require samples to be tagged, immobilized on a surface or otherwise modified. Fully automated, the computer-controlled syringe pumps mix, dilute and deliver samples, while the software controls data acquisition and results analysis. The system can be used to characterize weak and strong interactions, to analyze simple or complex association stoichiometries, to determine molar mass and to provide equilibrium dissociation constants from picomolars to millimolars. It can be used by the pharmaceutical and biotechnology industries to study the composition dependence of measurable solution properties.