The routine iodination methods are easy to lead to biological inactivation of cytokines, which is one of reasons for failure of ligand receptor binding assay. By using two-phase iodination of chromine-T, rhG-CSF and rhEPO were iodinated with Na¹²⁵I and the characteristic of EPO receptor in BET-2 cell and G-CSF receptor in NFS-60 cell were observed by receptor ligand binding assay. It was showed that the radioactivity of ¹²⁵I-G-CSF and ¹²⁵I-EPO were much higher than that obtained by other methods and it was found that there are high and low affinity EPO receptors in BET-2 cells and one high affinity G-CSF receptor in NFS-60 cells. These results are in accord with literature data. It suggests that the two-phase iodination of chromine-T is an ideal method to iodinate cytokines.