1. The antidiuretic effects of oral therapy with benzothiadiazine and phthalimidine diuretics have been studied in seven patients with diabetes insipidus of pituitary origin.
2. The immediate and chronic phases of diuretic-induced antidiuresis differ in their characteristics. Immediate antidiuresis is closely related both to the saluretic action of the diuretics and to the level of fluid turnover prevailing before their administration. By contrast, the findings in four patients maintained on polythiazide or clorexolone for at least 4 years show that antidiuresis persists at a time when saluretic effects have ceased and there is no longer any detectable disturbance in body sodium metabolism. A change in mechanism of antidiuresis appears to occur with the passage of time.
3. There is a parallelism between the characteristics of the chronic antidiuretic and antihypertensive actions of diuretics. The mechanism of both effects remains obscure.
4. Despite uncertainty as to mechanism, diuretic therapy offers a reliable means of treating diabetes insipidus on a long-term basis. The only complication encountered was symptomless hypokalaemia which developed despite regular use of supplemental oral potassium. Combined administration of triamterene or amiloride with either polythiazide or clorexolone has been used with success as an alternative regime.