Three cases of dilutional hyponatremia are presented. All had ADH bio-assay at the height of biochemical abnormality and the values were found to be normal. The first two cases were due to cortisol deficiency. An interesting feature of these two cases was a high exchangeable sodium which was corrected by administration of cortisone, suggesting that cortisol plays some part in the distribution of sodium between the extracellular and the intracellular space. The third case occurred in association with urinary tract infection. Similar findings have been reported in elderly patients with pneumonia and have been presumed to be due to inappropriate secretion of ADH on indirect evidence. ADH assay has rarely been done and has never been found to be high. On the basis of the findings observed in the three cases, it is suggested that factors other than ADH excess and cortisol deficiency are involved in the production of dilutional hyponatremia.