This text is a summary of basic principles and techniques and is dedicated to all those students who have been told by their mentors, "Go forth and do two-dimensional gels and have the results on my desk tomorrow. " No attempt has been made in this text to provide exhaustive lists of references related to basic principles or techniques or to list every com pany or supplier involved in this area of research. Nevertheless, it is hoped that sufficient information is given to help a new investigator or student appreciate the complexities but develop sufficient expertise to carry out these techniques successfully. The discussions are designed to instill in basic science and clinical investigators of all levels of expertise an appreciation of the power of combining a variety of techniques as well as to provide basic insight into the theories, complexities, and problems frequently encountered with electrophoretic and immunochemical meth ods. Bonnie S. Dunbar Houston v Acknowledgments I wish to thank my students and staff for their patience and support throughout the preparation of this text. I would like to acknowledge my appreciation for my extensive discussions with Dr. David Sammons (Uni versity of Arizona) and to Dr. N. L. and Dr. N. G. Anderson and their colleagues (Argonne National Laboratory) for their invaluable advice and suggestions in this area over the years. I thank my research assistant, Ms.