Human BMP-4 immunoassay is a 3.5 - 4.5 hour solid phase ELISA designed to measure Human BMP-4 in cell culture supernates, serum and EDTA plasma. It contains recombinant Human BMP-4 and antibodies raised against this protein. It has been shown to accurately quantitie recombinant Human BMP-4. Results obtained with naturally occurring BMP-4 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 BMP-4.