The effects of hypertonic saline infusion into the third ventricle were investigated in ten monkeys which were pre-operated, trained, and used in the conscious state under controlled conditions. 2. In non-hydrated monkeys, intraventricular infusion of NaCl 1.0 M, 0.01 ml./min for 30 min did not affect urine volume or Na output but produced a small increase in urine osmolality. Comparable infusion of NaCl 0.15 M had no effect on any parameter. 3. In monkeys undergoing water diuresis (with i.v. infusion of 5% dextrose), intraventricular hypertonic saline produced large reciprocal changes in urine volume and osmolality while urine Na showed no significant change. The effects on urine volume and osmolality were greater than those of lysine-vasopressin 30 m-u./kg i.v. 4. The absence of natriuresis after intraventricular hypertonic saline infusion in the monkey was in notable contrast to the results reported in lower species. However, the data suggested that the infusion probably released ADH as in other species.
