Three patients with diabetes insipidus manifested allergic reactions to various antidiuretic hormone preparations of animal origin. After using vasopressin (Pitressin) tannate in oil, one patient had an extensive skin eruption and another had marked tenesmus and constipation. The third patient had allergic rhinitis and asthma after using posterior pituitary snuff. In all three patients, the use of lypressin (lysine-8-vasopressin) led to good control of their diabetes insipidus, and its use was not attended by any allergic symptoms or other side effects.