The effect of pulse parameters (duty and frequency) in a constant direct current iontophoresis on the antidiuretic response (elevation in rat urinary osmotic pressure) of desmopressin acetate (DDAVP) was examined in diabetes insipidus rats. Although antidiuretic response was not affected by frequency, it was induced by a duty of more than 26% and prolonged with increasing duty. A positively relationship between dose and AUC, the area under the osmotic pressure-time curve, was confirmed by intravenous administration of DDAVP, and the AUC induced by the iontophoretic delivery increased with increasing duty. The voltage across rat skin required to maintain a constant current density was investigated. A higher voltage was initially applied rat skin in a higher duty. This was related the prolonged pharmacological response induced by iontophoresis.