The surface plasmon resonance (SPR) biosensor method has emerged as a very flexible and powerful approach for detecting a wide diversity of biomolecular interactions. SPR monitors molecular interactions in real time and provides significant advantages over optical or calorimetric methods for systems with strong binding and low spectroscopic signals or reaction heats. The SPR method simultaneously provides kinetic and equilibrium characterization of the interactions of biomolecules. Such information is essential for development of a full understanding of molecular recognition as well as for areas such as the design of receptor-targeted therapeutics. This article presents basic, practical procedures for conducting SPR experiments. Initial preparation of the SPR instrument, sensor chips, and samples are described. This is followed by suggestions for experimental design, data analysis, and presentation. Steady-state and kinetic studies of some small molecule-DNA complexes are used to illustrate the capability of this technique. Examples of the agreement between biosensor-SPR and solution studies are presented.