An insulin analog comprises a B-chain polypeptide incorporating a chlorinated phenylalanine. The chlorinated phenylalanine may be located at position B24. The chlorinated phenylalanine may be para-monochloro-phenylalanine. The analog may be of a mammalian insulin, such as human insulin. A nucleic acid encodes such an insulin analog. The chlorinated insulin analogs retain significant activity. A method of treating a patient comprises administering a physiologically effective amount of the insulin analog or a physiologically acceptable salt thereof to a patient. Chlorine substitution-based stabilization of insulin may reduce fibrillation and thereby enhance the treatment of diabetes mellitus in regions of the developing world lacking refrigeration.
