The Quantikine Rat IL-6 Immunoassay is a 4.5 hour solid phase ELISA designed to measure IL-6 levels in cell culture supernates, serum, and plasma. It contains E. coli-expressed recombinant rat IL-6 and antibodies raised against recombinant rat IL-6. This immunoassay has been shown to accurately quantitate the recombinant factor. Results obtained using natural rat IL-6 showed dose response curves that were parallel to the standard curves obtained using the recombinant Quantikine kit standards. These results indicate that this kit can be used to determine relative mass values for natural rat IL-6