Since the classical work of Rosalyn Yalow and Solomon Berson on the radioim- munoassay of insulin in the late 1950s, which so brilliantly opened new domains in the diagnostics sector, immunoassays have been well received as a diagnostic and research tool in several disciplines of life sciences. The economics, rapidity, sensitivity, specificity, and the easy-to-use approach of immunodiagnostic tests are widely recognized, and have had a tremendous impact on clinical, agricultural, food, veterinary, and environmental diagnostics. At present, in the clinical diag- nostic sector alone, immunoassay products command an annual worldwide mar- ket value in excess of U. S. $10 billion, which is expanding by about 10% per annum. The recent trend toward increasing demand for automation of immunoassays and stable reagents clearly shows a definitive shift to nonisotopic immunoassay systems on a large scale. Historically, enzyme immunoassays have been in a prime position for in-house applications, primarily because of the easy access to inex- pensive measuring equipment as well as to a vast body of literature on labeling techniques and applications. The recent popularity with the general public of sev- eral over-the-counter immunoassay products based on this technology, such as glucose level kits for diabetics, cholesterol screening tests, and pregnancy detec- tion test kits, is quite evident.