[Past, present and future of enzyme immunoassay]

Enzyme immunoassay (EIA) is one of the most popular non-isotopic immunoassay methods, with various clinical applications. After radioimmunoassay was developed by Yalow and Berson, its competitive binding principle was combined with enzyme labeling techniques and its application has been expanded by developing various procedures. Theoretically, EIA is more sensitive than RIA, being able to measure levels as minute as some attomole levels. Automated enzyme immunoassay systems have further improved its intra-laboratory variation, but relatively large variations among different reagent kits must be improved. Highly sensitive EIA systems should allow wider clinical applications.