NEDO, Shimadzu Co., AIST, Kyoto Monotech Co., and JBA have jointly developed a protein array system which assesses optimum ligands for purification of various antibody drugs. The protein array is set into a flow-cell ⁽¹⁾, so that solutions can pass through the inside of the array-matrix. Then UV light is applied to the protein array and transmitted light is monitored by a CCD camera to observe antibody directly without labeling ⁽²⁾. It is observed that UV absorption at each spot increases when an antibody solution is applied, and decreases when an acidic elution buffer is applied, showing antibody binding to ligands and dissociation from ligands ⁽³⁾. Quantified UV absorption at each spot shows that dissociation speed of antibody greatly varies among the ligands ⁽⁴⁾. So, this array system enables high-throughput analysis of ligands' properties and assessment of optimum ligands for purification. Using this array system, we are attempting to establish methods to improve purification processes for the safe and cost-effective antibody drugs.