The Human TGF-beta 1 Immunoassay is a 4.5 hour solid phase ELISA designed to measure TGF-beta 1 in acid activated cell culture supernates, serum, plasma, and urine. It contains recombinant human TGF-beta 1 expressed by CHO cells and has been shown to quantitate the recombinant factor accurately. Results obtained using natural TGF-beta 1 showed linear curves that were parallel to the standard curves obtained using the recombinant kit standards. These results indicate that this kit will provide accurate quantitation for both recombinant and natural human TGF-beta 1.