Here is an up-to-date review of important new methods and results in <i>anti-idiotypes, receptors, and molecular mimicry.</i> <i>It begins with a discussion of the theoretical background of</i> <i>the anti-idiotypic network, its role in the regulation of </i> <i>immune response, and the physical characteristics of </i> <i>anti-idiotypic antibodies. It then goes on to explore many </i> <i>exciting applications in such areas as insulin action, </i> <i>thyroid cell function, the neurosciences, cardiology, </i> <i>virology, pharmacology, and reproduction. </i>