Multiangle laser light scattering (MALLS) and sedimentation equilibrium are two powerful techniques used to characterize the association properties of proteins and their interactions in solution under physiological conditions. Both techniques have undergone a resurgence as a result of the advent of recombinant technologies which has enabled the generation of reasonable quantities of biologically significant proteins that exist in vivo in small amounts so that they can now be characterized physicochemically. As well, new technical developments with both techniques have made them much more sensitive and user friendly. In the case of static light scattering, this includes the use of lasers and modern detectors on-line with size exclusion chromatography so that one can establish absolute molecular weights of individual protein fractions eluting from the column. With sedimentation equilibrium, the Optima XL-I centrifuge (developed by Beckman, Palo Alto, CA) is equipped with both a new photoelectric scanning absorption optical system enabling exact measurement of concentration profiles at wavelengths of 190-800 nm and an interference optical system allowing the measurement of much higher concentration gradients. In both cases, powerful computer programs have been developed for data evaluation. Examples of the use of both techniques to study the association properties of cadherin in the presence and absence of calcium are described later.