A polypeptide having binding specificity for IL-23p19 or IL-17A and IL-23p19, wherein the polypeptide comprises a lipocalin mutein that binds with a detectable affinity to IL-23p19, (a) wherein the lipocalin mutein is a mutein of mature human tear lipocalin (SEQ ID NO: 1) comprising a mutated amino acid residue at ten or more positions corresponding to positions 26-34, 55-58, 60-61, 64, 101, 104-108, 111, 114 and 153 of the linear polypeptide sequence of the mature human tear lipocalin (SEQ ID NO: 1), wherein the mutated amino acid residues are selected from the group consisting of Arg 26 → Asp, Thr, Ser, Gly, Phe, Tyr, Val or Trp; Glu 27 → Thr, Asn, Asp, Trp, Arg, Val, Phe or Gln; Pro 29 → Arg, Ala, Ser, Glu, Leu or Thr; Glu 30 → Gly, Lys, Phe, His, Trp or Asn; Met 31 → Ala, His, Leu, Val, Trp, Gly, Pro or Asp; Asn 32 → Tyr, Trp, Gln, His, Leu, Ser, Phe or Asp; Leu 33 → Gln, Asp, Gly, Val, Glu, Ile or Phe; Glu 34 → Gly, Asn, Pro, Trp, Arg or His; Met 55 → Gln, Asn, Ile, Thr, Ser or Leu; Leu 56 → Pro, Ser, Phe, Tyr, Arg, Asn, Ala, Val, Asp, Gln, Glu or Thr; Ile 57→ Leu, Trp or Ser; Ser 58 → Asp, Trp, Phe, Ala, Glu, His, Arg, Pro or Gly; Arg 60 → Tyr, Asp, Thr, Phe, Ile, Ser or Leu; Cys 61 → Arg, Ser, Gly, Ala, Trp, Lys, Tyr, Asp, Thr, Val, Ile, Thr, Phe, Asn, Leu, Gln or Glu; Val 64 → Glu, Leu, Asp, or Ala; Cys 101 → Ser; Glu 104 → Trp, Thr, Ser, His, Ile, Arg or Ala; His 106 → Ala, Tyr, Phe, His, Thr or Glu; Gly 107→ Leu or Asp; Lys 108 → Arg, Ser, His, Gln or Trp; Arg 111 → Pro; and Lys 114 → Trp, wherein the lipocalin mutein has at least 85% identity to an amino acid sequence selected from the group consisting of SEQ ID NOs: 6, 12, and 13, or a fragment thereof, or (b) wherein the lipocalin mutein is a mutein of mature human neutrophil gelatinase-associated lipocalin (hNGAL) (SEQ ID NO: 8) comprising ten or more mutated amino acid residue at one or more positions corresponding to positions 28, 36, 40-41, 49, 52, 68, 70, 72-73, 77, 79, 81, 87, 96, 100, 103, 106, 125, 127, 132 and 134 of the linear polypeptide sequence of mature hNGAL (SEQ ID NO: 8), wherein the mutated amino acid residues are selected from the group consisting of Gln 28 → His, Asp or Ala; Leu 36 → Asp, Gln, Glu, Met or Ser; Ala 40 → Arg, Leu or Tyr; Ile 41 → Met or Leu; Gln 49 → Met, Thr, Arg or Asp; Tyr 52 → Ser, Thr or Glu; Ser 68 → Trp, Arg or Thr; Leu 70 → Ile, Glu or Asp; Arg 72 → Ser, Pro, Ile or Asp; Lys 73 → His, Phe, Met or Thr; Asp 77 → Glu, Lys, Trp or Leu; Trp 79 → Thr, Pro, Ser or Gln; Arg 81 → Ala, Gly or Thr; Cys 87 → Ser or Thr; Asn 96 → Arg, Gly or His; Tyr 100 → Gly or Met; Leu 103 → Lys, Met or Asp; Tyr 106 → Phe; Lys 125 → Leu, His, or Tyr; Val 126 → Ala; Ser 127 → Glu, Tyr or Asp; Tyr 132 → Ser, Phe or His; and Lys 134 → Ala, Glu or Ser, wherein the lipocalin mutein has at least 85% identity to an amino acid sequence selected from the group consisting of SEQ ID NOs: 9, 10, and 15, or a fragment thereof. (a) wherein the lipocalin mutein is a mutein of mature human tear lipocalin (SEQ ID NO: 1) comprising a mutated amino acid residue at ten or more positions corresponding to positions 26-34, 55-58, 60-61, 64, 101, 104-108, 111, 114 and 153 of the linear polypeptide sequence of the mature human tear lipocalin (SEQ ID NO: 1), wherein the mutated amino acid residues are selected from the group consisting of Arg 26 → Asp, Thr, Ser, Gly, Phe, Tyr, Val or Trp; Glu 27 → Thr, Asn, Asp, Trp, Arg, Val, Phe or Gln; Pro 29 → Arg, Ala, Ser, Glu, Leu or Thr; Glu 30 → Gly, Lys, Phe, His, Trp or Asn; Met 31 → Ala, His, Leu, Val, Trp, Gly, Pro or Asp; Asn 32 → Tyr, Trp, Gln, His, Leu, Ser, Phe or Asp; Leu 33 → Gln, Asp, Gly, Val, Glu, Ile or Phe; Glu 34 → Gly, Asn, Pro, Trp, Arg or His; Met 55 → Gln, Asn, Ile, Thr, Ser or Leu; Leu 56 → Pro, Ser, Phe, Tyr, Arg, Asn, Ala, Val, Asp, Gln, Glu or Thr; Ile 57→ Leu, Trp or Ser; Ser 58 → Asp, Trp, Phe, Ala, Glu, His, Arg, Pro or Gly; Arg 60 → Tyr, Asp, Thr, Phe, Ile, Ser or Leu; Cys 61 → Arg, Ser, Gly, Ala, Trp, Lys, Tyr, Asp, Thr, Val, Ile, Thr, Phe, Asn, Leu, Gln or Glu; Val 64 → Glu, Leu, Asp, or Ala; Cys 101 → Ser; Glu 104 → Trp, Thr, Ser, His, Ile, Arg or Ala; His 106 → Ala, Tyr, Phe, His, Thr or Glu; Gly 107→ Leu or Asp; Lys 108 → Arg, Ser, His, Gln or Trp; Arg 111 → Pro; and Lys 114 → Trp, wherein the lipocalin mutein has at least 85% identity to an amino acid sequence selected from the group consisting of SEQ ID NOs: 6, 12, and 13, or a fragment thereof, or (b) wherein the lipocalin mutein is a mutein of mature human neutrophil gelatinase-associated lipocalin (hNGAL) (SEQ ID NO: 8) comprising ten or more mutated amino acid residue at one or more positions corresponding to positions 28, 36, 40-41, 49, 52, 68, 70, 72-73, 77, 79, 81, 87, 96, 100, 103, 106, 125, 127, 132 and 134 of the linear polypeptide sequence of mature hNGAL (SEQ ID NO: 8), wherein the mutated amino acid residues are selected from the group consisting of Gln 28 → His, Asp or Ala; Leu 36 → Asp, Gln, Glu, Met or Ser; Ala 40 → Arg, Leu or Tyr; Ile 41 → Met or Leu; Gln 49 → Met, Thr, Arg or Asp; Tyr 52 → Ser, Thr or Glu; Ser 68 → Trp, Arg or Thr; Leu 70 → Ile, Glu or Asp; Arg 72 → Ser, Pro, Ile or Asp; Lys 73 → His, Phe, Met or Thr; Asp 77 → Glu, Lys, Trp or Leu; Trp 79 → Thr, Pro, Ser or Gln; Arg 81 → Ala, Gly or Thr; Cys 87 → Ser or Thr; Asn 96 → Arg, Gly or His; Tyr 100 → Gly or Met; Leu 103 → Lys, Met or Asp; Tyr 106 → Phe; Lys 125 → Leu, His, or Tyr; Val 126 → Ala; Ser 127 → Glu, Tyr or Asp; Tyr 132 → Ser, Phe or His; and Lys 134 → Ala, Glu or Ser, wherein the lipocalin mutein has at least 85% identity to an amino acid sequence selected from the group consisting of SEQ ID NOs: 9, 10, and 15, or a fragment thereof.