Management of postoperative diabetes insipidus (DI) frequently requires intermittent treatment with multiple subcutaneous injections of pituitrin or vasopressin, in doses averaging 20 IU/24 h. Use of a syringe pump for a continuous infusion of ultralow doses of pituitrin produced uniform, constant, and sustained reduction of urinary output, thus facilitating regular fluid replacement. Twelve patients with postoperative DI received iv pituitrin at a dose of 1.6 ± 0.26 mIU/kg·h (1 to 2 IU/24 h). The antidiuretic effect began at the third hour of treatment, peaked by the sixth hour (diuresis of 37 ml/h, specific gravity of 1.018 ± 0.002), and was sustained throughout infusion. Polyuria recurred 3 h after the infusion was discontinued; this rapid reversibility is highly advantageous when excessive fluid intake causes overhydration. Pressor effects were not observed during the treatment period.