An insulin analogue comprising a B-chain polypeptide incorporating a halogenated phenylalanine at position B24, B25 or B26. The analogue may be of a mammalian insulin such as human insulin. A nucleic acid encoding such an insulin analogue. Some halogenated insulin analogues retain significant activity. Medical uses of the insulin analogues for treating a patient comprises administering a physiologically effective amount of the insulin analogue or a physiologically acceptable salt thereof to a patient. Halogen substitution-based stabilisation of insulin may enhance the treatment of diabetes mellitus in regions of the developing world lacking refrigeration. The preferred analogue is an insulin analogue comprising a B-chain polypeptide incorporating a pentafluoro-phenylalanine (5F-Phe) at position B24.
