Human Soluble ST2/IL-1R4 immunoassay is a 3.5 - 4.5 hour solid phase ELISA designed to measure Human ST2 in serum, and plasma. It contains recombinant Human ST2 and antibodies raised against this protein. It has been shown to accurately quantitie recombinant Human ST2. Results obtained with naturally occurring ST2 samples showed linear curves that were parallel to the standard curves obtained using the kit standards. These results indicate that the Immunoassay kit can be used to determine relative mass values for natural Human ST2.