Human histidine-rich glycoprotein (HRG) is a multidomain, monomeric, secreted, 67-75 kDa member of the cystatin superfamily of molecules. Its name derives from the fact that 26% of its amino acids (aa) are histidine and proline. In human, it is synthesized as a 525?aa precursor that contains an 18 aa signal sequence and a 507 aa mature region. Five distinct domains are recognized in the mature molecule. As HRG has the function of cell adhesion, we measure the activity of recombinant human HRG by the ability of the immobilized protein to support the adhesion of con-A activated MOLT4 human acute lymphoblastic leukemia cells. When 1 x 105?cells/well with 7.5 ug/ml conA are added to recombinat human HRG coated plates (0.1 μg/mL with 100 μL/well), >70% cells will adhere after 2?hour incubation at 37 ℃. The adhesion of MOLT-4 after 2?hour incubation at 37 ℃ observed by inverted microscope was shown in Figure 1.