Growth Hormone (GH), also known as somatotropin, is a member of a family of growth factors. Human growth hormone is a 191 amino acid single-chain polypeptide produced via the anterior pituitary of the brain in the acidophilic, somatotrophic cells. Its production is tightly regulated through several complex feedback mechanisms in response to stress, exercise, nutrition, sleep, and growth hormone itself. Annexin A2 (ANXA2) has been shown to play multiple roles in growth, development, metabolism and ANXA2 is a high affinity receptor for GH. Thus a functional binding ELISA assay was conducted to detect the interaction of recombinant human GH and recombinant human ANXA2. Briefly, GH was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to ANXA2-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-GH pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody for 1h at 37℃, wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50 µl stop solution to the wells and read at 450/630 nm immediately. The binding activity of recombinant human GH and recombinant human ANXA2 was shown in Figure 1, the EC50 for this effect is 2.1 ug/mL.