Immunoassays based on the formation of antibodyhormone conjugates have been widely used in clinical chemistry for the determination of hormones. In this field radioimmunoassays have been extensively applied since 1960. Although extremely sensitive and quite precise, these assays have several drawbacks. In recent years, alternative methods used enzymes, chemiluminescent and fluorescent substances as labels have been developed. By the use of Eulabelled antibody or hormone, and time - resolved fluorescence measurement, new possibilities towards more, sensitive immunoassays have been opened. Keywords :