A method for determining the binding of an antibody, which comprises a first binding site specifically binding to a first antigen and a second binding site specifically binding to a second antigen, to said first and said second antigen, wherein the method comprises the following steps: a) capturing the antibody on a solid phase using a capture reagent specifically binding to a constant domain of the antibody, b) incubating the captured antibody with the first or the second antigen in a buffer comprising 1 mM KH2PO4, 10 mM Na2HPO4, 137 mM NaCl, 2.7 mM KCl, pH 7.4, 0.05% Tween-20 and 300 mM NaCl to form a captured antibody-antigen complex and determining a first binding signal, c) either incubating the captured antibody-antigen complex with the antigen not used for the formation of the captured antibody-antigen complex to form a captured antibody-antigen-antigen complex and determining a second binding signal, or regenerating the surface, capturing the antibody on a solid phase using a capture reagent specifically binding to a constant domain of the antibody, incubating the captured antibody with the antigen not used for the formation of the captured antibody-antigen complex in step b) in the same buffer as in step b) to form a captured antibody-antigen complex and determining a third binding signal, and d) determining the overall or individual binding of the antibody to the first and the second antigen from the first binding signal and the second or third binding signal, wherein the solid phase is a surface plasmon resonance chip, the first binding signal is a surface plasmon resonance response and the second binding signal is a surface plasmon resonance response. a) capturing the antibody on a solid phase using a capture reagent specifically binding to a constant domain of the antibody, b) incubating the captured antibody with the first or the second antigen in a buffer comprising 1 mM KH2PO4, 10 mM Na2HPO4, 137 mM NaCl, 2.7 mM KCl, pH 7.4, 0.05% Tween-20 and 300 mM NaCl to form a captured antibody-antigen complex and determining a first binding signal, c) either incubating the captured antibody-antigen complex with the antigen not used for the formation of the captured antibody-antigen complex to form a captured antibody-antigen-antigen complex and determining a second binding signal, or regenerating the surface, capturing the antibody on a solid phase using a capture reagent specifically binding to a constant domain of the antibody, incubating the captured antibody with the antigen not used for the formation of the captured antibody-antigen complex in step b) in the same buffer as in step b) to form a captured antibody-antigen complex and determining a third binding signal, and incubating the captured antibody-antigen complex with the antigen not used for the formation of the captured antibody-antigen complex to form a captured antibody-antigen-antigen complex and determining a second binding signal, or regenerating the surface, capturing the antibody on a solid phase using a capture reagent specifically binding to a constant domain of the antibody, incubating the captured antibody with the antigen not used for the formation of the captured antibody-antigen complex in step b) in the same buffer as in step b) to form a captured antibody-antigen complex and determining a third binding signal, and d) determining the overall or individual binding of the antibody to the first and the second antigen from the first binding signal and the second or third binding signal, wherein the solid phase is a surface plasmon resonance chip, the first binding signal is a surface plasmon resonance response and the second binding signal is a surface plasmon resonance response. <EOS>