A radioligand receptorassay for serum HCG.

A radioligand receptorassay system is described for the measurement of human choriogonadotrophin (HCG) in serum, using 600-1600 X g fractions of homogenates of superovulating rat ovaries. The method is specific for HCG and lutrophin (LH), with a detection limit of 3.5 mIU HCG. The values obtained in the dilutions of pregnancy sera paralleled the standard curve up to 20 microliter, and no non-specific effects were found with this amount of serum. The potency ratio R/I, measured in normal pregnancy sera by radioligand receptorassay and radioimmunoassay, varied between 1.1 and 3.2. No relationship was found between the stage of pregnancy and the R/I ratio.