A single chain insulin analogue comprising: (A) the A-chain of human or animal insulin, or an analogue thereof which is a variant wherein (a) one amino acid residue is replaced by a naturally or non-naturally occurring amino acid, (b) the order of two amino acid residues is reversed, or (c) both (a) and (b) are present together; (B) the B-chain of human or animal insulin, or an analogue thereof which is a variant wherein (a) one amino acid residue is replaced by a naturally or non-naturally occurring amino acid, (b) the order of two amino acid residues is reversed, or (c) both (a) and (b) are present together; (C) (i) an intermolecular disulfide bond between the cysteine in position 7 of the insulin A-chain and the cysteine in position 7 of the insulin B-chain; (ii) an intermolecular disulfide bond between the cysteine in position 20 of the insulin A-chain and the cysteine in position 19 of the insulin B-chain; (iii) an intramolecular disulfide bond between the cysteine in position 6 and the cysteine in position 11 of the insulin A-chain; and (D) a further covalent link, L, between the carboxyl terminal amino acid of said A-chain of human or animal insulin, or analogue thereof, with the side chain of the lysine residue in position 29 of said B-chain of human or animal insulin, or analogue thereof, wherein the further covalent link, L, is a direct bond; wherein said single chain insulin analogue performs the same action as human insulin in terms of glycemic control. (A) the A-chain of human or animal insulin, or an analogue thereof which is a variant wherein (a) one amino acid residue is replaced by a naturally or non-naturally occurring amino acid, (b) the order of two amino acid residues is reversed, or (c) both (a) and (b) are present together; (B) the B-chain of human or animal insulin, or an analogue thereof which is a variant wherein (a) one amino acid residue is replaced by a naturally or non-naturally occurring amino acid, (b) the order of two amino acid residues is reversed, or (c) both (a) and (b) are present together; (C) (i) an intermolecular disulfide bond between the cysteine in position 7 of the insulin A-chain and the cysteine in position 7 of the insulin B-chain; (ii) an intermolecular disulfide bond between the cysteine in position 20 of the insulin A-chain and the cysteine in position 19 of the insulin B-chain; (iii) an intramolecular disulfide bond between the cysteine in position 6 and the cysteine in position 11 of the insulin A-chain; and (i) an intermolecular disulfide bond between the cysteine in position 7 of the insulin A-chain and the cysteine in position 7 of the insulin B-chain; (ii) an intermolecular disulfide bond between the cysteine in position 20 of the insulin A-chain and the cysteine in position 19 of the insulin B-chain; (iii) an intramolecular disulfide bond between the cysteine in position 6 and the cysteine in position 11 of the insulin A-chain; and (D) a further covalent link, L, between the carboxyl terminal amino acid of said A-chain of human or animal insulin, or analogue thereof, with the side chain of the lysine residue in position 29 of said B-chain of human or animal insulin, or analogue thereof, wherein the further covalent link, L, is a direct bond; <EOS>