A diabody molecule comprising a first polypeptide chain and a second polypeptide chain, wherein said first polypeptide chain and said second polypeptide chain are covalently linked to one another, with the proviso that the covalent link is not a peptide bond, wherein: said first polypeptide chain comprises: (i) a first domain comprising a binding region of a light chain variable domain of a first immunoglobulin specific for a first epitope, (ii) a second domain comprising a binding region of a heavy chain variable domain of a second immunoglobulin specific for a second epitope, and (iii) a third domain comprising at least one cysteine residue, and an E-coil separator having the amino acid sequence of SEQ ID NO:299 or a K-coil separator having the amino acid sequence of SEQ ID NO:300, which first domain and second domain are covalently linked such that the first domain and second domain do not associate to form a first epitope binding site; said second polypeptide chain comprises: (i) a fourth domain comprising a binding region of a light chain variable domain of the second immunoglobulin specific for said second epitope, (ii) a fifth domain comprising a binding region of a heavy chain variable domain of the first immunoglobulin specific for said first epitope, and (iii) a sixth domain comprising at least one cysteine residue, and an E-coil separator having the amino acid sequence of SEQ ID NO:299 or a K-coil separator having the amino acid sequence of SEQ ID NO:300, which fourth domain and fifth domain are covalently linked such that the fourth domain and fifth domain do not associate to form an epitope binding site; wherein said cysteine residue of said third and sixth domains form a disulfide bond between said first and second polypeptide chains; wherein when said first polypeptide chain comprises said E-coil separator, said second polypeptide chain comprises said K-coil separator; and when said first polypeptide chain comprises said K-coil separator, said second polypeptide chain comprises said E-coil separator; wherein the first domain and the fifth domain associate to form a first binding site that binds said first epitope; wherein the second domain and the fourth domain associate to form a second binding site that binds said second epitope; and wherein either: (i) said first epitope is an epitope of CD32B and said second epitope is an epitope of CD79b, or (ii) said first epitope is an epitope of CD79b and said second epitope is an epitope of CD32B. said first polypeptide chain comprises: (i) a first domain comprising a binding region of a light chain variable domain of a first immunoglobulin specific for a first epitope, (ii) a second domain comprising a binding region of a heavy chain variable domain of a second immunoglobulin specific for a second epitope, and (iii) a third domain comprising at least one cysteine residue, and an E-coil separator having the amino acid sequence of SEQ ID NO:299 or a K-coil separator having the amino acid sequence of SEQ ID NO:300, which first domain and second domain are covalently linked such that the first domain and second domain do not associate to form a first epitope binding site; said second polypeptide chain comprises: (i) a fourth domain comprising a binding region of a light chain variable domain of the second immunoglobulin specific for said second epitope, (ii) a fifth domain comprising a binding region of a heavy chain variable domain of the first immunoglobulin specific for said first epitope, and (iii) a sixth domain comprising at least one cysteine residue, and an E-coil separator having the amino acid sequence of SEQ ID NO:299 or a K-coil separator having the amino acid sequence of SEQ ID NO:300, which fourth domain and fifth domain are covalently linked such that the fourth domain and fifth domain do not associate to form an epitope binding site; wherein said cysteine residue of said third and sixth domains form a disulfide bond between said first and second polypeptide chains; wherein when said first polypeptide chain comprises said E-coil separator, said second polypeptide chain comprises said K-coil separator; and when said first polypeptide chain comprises said K-coil separator, said second polypeptide chain comprises said E-coil separator; wherein the first domain and the fifth domain associate to form a first binding site that binds said first epitope; wherein the second domain and the fourth domain associate to form a second binding site that binds said second epitope; and wherein either: (i) said first epitope is an epitope of CD32B and said second epitope is an epitope of CD79b, or (ii) said first epitope is an epitope of CD79b and said second epitope is an epitope of CD32B.