1. Chlorpropamide, carbamazepine and clofibrate have an antidiuretic action in patients with neurohypophyseal diabetes insipidus which is qualitatively similar to that of antidiuretic hormone (ADH).
2. An additive antidiuretic effect is produced by combination of chlorpropamide and carbamazepine with small dosages of ADH.
3. After an immediate and transient antidiuresis, a single intravenous bolus injection of lysine vasopressin given during treatment with chlorpropamide, chlorpropamide with a continuous intravenous infusion of lysine vasopressin, carbamazepine or clofibrate, resulted in increased water diuresis for 12–24 h or longer.
4. This paradoxical diuresis was not observed during treatment with chlorothiazide.
5. It is suggested that the antidiuretic action of chlorpropamide, carbamazepine and clofibrate is localized at the receptor site for ADH in the distal renal tubular cell.