Although structural, biochemical, and genetic studies have provided much insight into the determinants of specificity and affinity of proteins for RNA, little is currently known about the kinetics that underlie RNA-protein interactions. Protein-RNA complexes are dynamic, and the kinetics of binding and release could influence many processes, such as the ability of RNA-binding proteins to compete for binding sites, the sequential assembly of ribonucleoprotein complexes, and the ability of bound RNA to move between cellular compartments. Therefore, to attain a complete and biologically relevant understanding of RNA-protein interactions, complex formation must be studied not only in equilibrated reactions, but also as a dynamic process. BIACORE, a surface plasmon resonance-based biosensor technology, allows intermolecular interactions to be measured in real time, and can provide both equilibrium and kinetic information about complex formation. This technology is a powerful tool with which to study the dynamics of RNA-protein interactions. We have used BIACORE extensively to obtain detailed insight into the interaction between RNA and proteins carrying RNA recognition motif domains. Here we discuss the physical principles on which BIACORE is based, and the required instrumentation. We describe how to design well-controlled RNA-protein interaction experiments aimed at yielding high-quality data, and outline the steps required for data analysis. In addition, we present examples to illustrate how kinetic studies have provided us with unique insights into the interaction of the spliceosomal U1A protein and the neuronal HuD protein with their respective RNA targets. (c) 2002 Elsevier Science (USA).