This test kit is an immunoradiometric assay (IRMA) based on coated-tubes with monoclonal antibodies directed against distinct epitopes of the molecule of SHBG. Two capture antibodies are coated on the inner wall of tubes. SHBG of the calibrators or of the samples is captured by these antibodies. Addition of the third antibody labeled with 125Iodine completes the system, allowing the formation of a bridge between the coated antibodies and the labeled antibody. After washing, the remaining radioactivity bound to the tubes is directly related to the concentration of SHBG in the calibrators or samples. The careful choice of the three monoclonal antibodies allows high specificity and high sensitivity and avoids excess of specificity which is sometimes reproached to immunometric assays with only two monoclonals. This test kit exists also under a form dedicated to R&D Pharmaceutical laboratories . This version (Q3) is available on special request only.