SUMMARY: 1. An investigation has been made of the effects of malnutrition produced by a diet of cassava on the adrenal cortex and hypothalamo-neurohypophysial system of rodents. 2. The renal response to isotonic saline was impaired in the malnourished animals. A reduction in adrenal ascorbic acid and in neurohypophysial pressor content also occurred. 3. In response to an intravenous isotonic saline load, adrenalectomized animals were unable to excrete as great a volume of urine as sham-operated controls, but no differences were detected in urinary sodium output. 4. In the malnourished animals, histochemical observation revealed a fall in adrenal alkaline phosphatase activity and impaired synthesis and secretion of neurosecretory material in the hypothalamo-neurohypophysial system. 5. From the evidence presented it is likely that the reduced renal response to isotonic saline in the malnourished animals reflects a disturbance in the adrenal cortex rather than increased secretion of antidiuretic hormone.