1. A patient with polyuria in whom diabetes insipidus had been diagnosed was treated with Pitressin. Resistance to this therapy developed after 18 months and a circulating antibody to vasopressin was then demonstrated. Withdrawal of therapy led to a fall in titre of the antibody and an increase in maximal urinary concentration.
2. The antibody to vasopressin was associated with the IgA fraction of the serum immunoglobulins and its characteristics are described.