Since they were first utilized, immunoassays have witnessed phenomenal growth in the range and scope of their applications. A vast array of different labels and assay strategies has been developed to meet the requirements of sensitivity, accuracy and convenience. The development of increasingly sensitive labels and detection equipment has seen a drastic improvement in the sensitivity of immunoassay systems, allowing an ever-increasing range of analytes to be measured accurately. At the same time, simple to use, inexpensive assay systems have been developed with the necessary reliability, accuracy and sensitivity to bring immunoassay technology to much more diverse areas such as home testing, near-patient monitoring, and large screening programmes in developing countries. Recent developments in molecular biology techniques have made possible the production of fusion antibody conjugates, which can lead to further improvements in sensitivity and cost of reagents, as well as possibly revolutionizing the production of monoclonal antibodies. However, dissatisfaction with various aspects of existing immunoassay technology will necessarily lead to the continued development of this already widely diverse subject.