An in vitro method for production of a full-length bispecific antibody comprising the following steps: a) incubating a first full-length antibody with a second full-length antibody under reducing conditions sufficient to allow reduction of the inter-chain disulfide bonds in the hinge region, and wherein the CH3 region of said first full-length antibody is a first CH3 region and has an Arg at position 409, and the CH3 region of said second full-length antibody is a second CH3 region and has: (i) an Asp, Glu, Gly, Asn, Arg, Ser, Thr, Val, or Trp at position 368; (ii) a Phe, His, Lys, Arg or Tyr at position 399; (iii) a Gly, Leu, Met or Trp at position 407 and a Lys at position 409, and wherein the first CH3 further has a Tyr at position 407; or (iv) an amino acid other than Phe, Arg or Gly at position 405 and has a Lys at position 409, and wherein the first CH3 further has a Phe at position 405, such that the sequences of said first and second CH3 regions are different and are such that the heterodimeric interaction between said first and second CH3 regions is stronger than each of the homodimeric interactions of said first and second CH3 regions, wherein the amino acid positions are numbered according to the EU-index as described in Kabat, wherein said first and second full-length antibodies bind different epitopes, wherein said first and second full-length antibodies: 1) each have an Fc region with an amino acid sequence that is of an IgG1 isotype; 2) each have an Fc region with an amino acid sequence that is of an IgG2 isotype; 3) each have an Fc region with an amino acid sequence that is of an IgG3 isotype; or 4) each have an Fc region with an amino acid sequence that is of an IgG4 isotype; and wherein said first and second antibodies are humanized antibodies or wherein said first and second antibodies each comprise a full-length heavy chain of a human antibody; and further wherein step a) comprises incubation for at least 90 minutes at a temperature of at least 20°C in the presence 2-mercaptoethylamine at a concentration of at least 25 mM; b) subjecting at least 10 mL of the composition obtained from step a) to oxidizing conditions sufficient to allow oxidation of cysteines in the full-length bispecific antibody to inter-chain disulfide bonds, and c) obtaining the full-length bispecific antibody. a) incubating a first full-length antibody with a second full-length antibody under reducing conditions sufficient to allow reduction of the inter-chain disulfide bonds in the hinge region, and wherein the CH3 region of said first full-length antibody is a first CH3 region and has an Arg at position 409, and the CH3 region of said second full-length antibody is a second CH3 region and has: (i) an Asp, Glu, Gly, Asn, Arg, Ser, Thr, Val, or Trp at position 368; (ii) a Phe, His, Lys, Arg or Tyr at position 399; (iii) a Gly, Leu, Met or Trp at position 407 and a Lys at position 409, and wherein the first CH3 further has a Tyr at position 407; or (iv) an amino acid other than Phe, Arg or Gly at position 405 and has a Lys at position 409, and wherein the first CH3 further has a Phe at position 405, such that the sequences of said first and second CH3 regions are different and are such that the heterodimeric interaction between said first and second CH3 regions is stronger than each of the homodimeric interactions of said first and second CH3 regions, wherein the amino acid positions are numbered according to the EU-index as described in Kabat, wherein said first and second full-length antibodies bind different epitopes, wherein said first and second full-length antibodies: 1) each have an Fc region with an amino acid sequence that is of an IgG1 isotype; 2) each have an Fc region with an amino acid sequence that is of an IgG2 isotype; 3) each have an Fc region with an amino acid sequence that is of an IgG3 isotype; or 4) each have an Fc region with an amino acid sequence that is of an IgG4 isotype; and wherein said first and second antibodies are humanized antibodies or wherein said first and second antibodies each comprise a full-length heavy chain of a human antibody; and further wherein step a) comprises incubation for at least 90 minutes at a temperature of at least 20°C in the presence 2-mercaptoethylamine at a concentration of at least 25 mM; (i) an Asp, Glu, Gly, Asn, Arg, Ser, Thr, Val, or Trp at position 368; (ii) a Phe, His, Lys, Arg or Tyr at position 399; (iii) a Gly, Leu, Met or Trp at position 407 and a Lys at position 409, and wherein the first CH3 further has a Tyr at position 407; or (iv) an amino acid other than Phe, Arg or Gly at position 405 and has a Lys at position 409, and wherein the first CH3 further has a Phe at position 405, 1) each have an Fc region with an amino acid sequence that is of an IgG1 isotype; 2) each have an Fc region with an amino acid sequence that is of an IgG2 isotype; 3) each have an Fc region with an amino acid sequence that is of an IgG3 isotype; or 4) each have an Fc region with an amino acid sequence that is of an IgG4 isotype; and b) subjecting at least 10 mL of the composition obtained from step a) to oxidizing conditions sufficient to allow oxidation of cysteines in the full-length bispecific antibody to inter-chain disulfide bonds, and c) obtaining the full-length bispecific antibody.