The 5X ELISA diluent solution is a Phosphate Buffered Solution supplemented with fetal bovine serum as a source of animal serum proteins. This buffer is used for blocking non-specific binding of ELISA plates, diluting recombinant standards and test samples, and making the working dilutions of the secondary detection reagent (i.e., detection antibody-biotin and AV-HRP Cat. No. 18-4100). This diluent solution also contains 1% ProClin 150 as a preservative.