Method for engineering an immunoglobulin comprising at least one modification in a structural loop region of said immunoglobulin and determining the binding of said immunoglobulin to an epitope of an antigen, wherein the unmodified immunoglobulin does not significantly bind to said epitope, comprising the steps of: - providing a nucleic acid encoding an immunoglobulin comprising at least one structural loop region, - modifying at least one nucleotide residue of at least one of said structural loop regions, - transferring said modified nucleic acid in an expression system, - expressing said modified immunoglobulin, - contacting the expressed modified immunoglobulin with an epitope, and - determining whether said modified immunoglobulin binds to said epitope, as well as modified immunoglobulins.
