A method for engineering an immunoglobulin having a variable domain and at least one modification in at least two structural loops of the immunoglobulin and determining the binding of the immunoglobulin to an epitope of an antigen, where the unmodified immunoglobulin does not significantly bind to said epitope, comprising the steps of providing a nucleic acid encoding an immunoglobulin having at least two structural loops, modifying at least one nucleotide residue of each of the structural loops, transferring the modified nucleic acid in an expression system, expressing the modified immunoglobulin, contacting the expressed modified immunoglobulin with an epitope, and determining whether the modified immunoglobulin binds to the epitope.