Binding kinetics help define how a medicine will communicate with physiology to produce a desired therapeutic response. Clinical efficacy, duration of action, clinical differentiation and safety may all be influenced by binding kinetics. The optimization of binding kinetics can be used to maximize a drug's therapeutic index and thereby decrease drug attrition. The gap between basic scientific principles and the potential medical value of a drug is currently bridged by the use of empirical assays. The value of binding kinetics to drug discovery will be increased through an improved ability to identify optimal kinetic mechanisms and define kinetic structure activity relationships.