At the present time, affinity capillary electrophoresis is a well-established method for the measurement of binding constants involving 1:1 interactions. Many recent applications of this technique have illustrated its versatility. If affinity capillary electrophoresis is to be widely applied to the study of all types of interactions it is imperative that we consider that higher order interactions may be present. Applying proper equations or developing new models appropriate to the description of such systems is essential to obtaining reliable binding information.