Wyatt Technology Corp. has released the Calypso, a composition-gradient multiangle light-scattering (CG-MALS) system that measures biomolecular interactions. It can determine both the affinity and binding stoichiometry for macromolecules in solution, with no need for sample tagging or immobilization that could influence the interaction. Calypso complements traditional MALS separation techniques, keeping the molecules in proximity to probe their interactions. The analyzer was used in conjunction with an online ultraviolet/visible concentration detector and the proprietary Dawn Heleos MALS instrument to provide rapid and precise measurements of the interaction between an antithrombin antibody and human thrombin. The equilibrium dissociation constant determined by the system agreed well with the manufacturer’s data as measured by ELISA.