An enzyme immunoassay for the quantitative measurement of free beta subunit of human chorionic gonadotropin (free Beta-hCG) in serum and plasma. Human Chorionic Gonadotropin (hCG) is a glycoprotein hormone normally produced by placenta during pregnancy. The hormone is present in blood and urine around seven to thirteen days following implantation of the fertilized ovum. Structurally intact hCG molecules consist of two non-covalently linked polypeptide subunits, the alpha and beta chain subunits. Measurement of intact hCG and of the alpha subunit of hCG appears to give similar results in blood and urine but not the levels of beta subunit. The measurement of free Beta-HCG in the first trimester of pregnancy has been reported as a useful marker in antenatal screening for Down Syndrome and other fetal aneuploidies. Increased free Beta-HCG values in combination with maternal age, the measurement of PAPP-A and the ultrasonic determination of nuchal translucency (NT) in pregnancy weeks 11 to 14 may detect up to 90 % of pregnancies with Down syndrom (reference 15).The DRG free Beta-HCG ELISA EIA-4718 may be used for the risk assessment of Down´s syndrom (trisomy 21) in the first trimester of pregnancy. For the risk assessment of trisomy 21 and other fetal aneuploidies free beta HCG should always be measured in combination with other analytes (for example PAPP-A and NT, see above) and a special software for the risk assessment of trisomy 21. According to the IVD Directive (98/79/EC) both software and kits for the additional analytes must be suitable for trisomy 21 screening and CE-certified by a notified body, indicated by the identification number of the notified body on the CE-mark on software and kits. The DRG Free Beta-HCG ELISA Kit is a solid phase enzyme-linked immunosorbent assay (ELISA) based on the sandwich principle. The microtiter wells are coated with a monoclonal [mouse] antibody directed towards a unique antigenic site on a Free Beta-hCG molecule. An aliquot of patient sample containing endogenous Free Beta-hCG is incubated in the coated well with enzyme conjugate, which is an anti-Beta-HCG antibody [rabbit] conjugated with horseradish peroxidase. After incubation the unbound conjugate is washed off. The amount of bound peroxidase is proportional to the concentration of Free Beta-HCG in the sample. Having added the substrate solution, the intensity of colour developed is proportional to the concentration of Free Beta-HCG in the patient sample.