Deranged adrenal cortical function was previously described in different stress situations. The aim of this work was to study the plasma cortisol and aldosterone levels in acute renal failure induced by the uranyl nitrate injection or bilateral ureteral ligation. In both groups of uremic dogs on the first day of uremia there was a significant elevation of the plasma cortisol level, being more pronounced and lasting longer after bilateral ureteral ligation. In sham operated controls a modest elevation was recorded. The plasma aldosterone level rose significantly from the first day in both groups of uremic animals. A further progressive elevation continued the following days and a highly elevated aldosterone levels remained until the end of the experiments. A minor but significant elevation of plasma aldosterone was also found in sham operated controls. This study has established increased plasma cortisol and aldosterone levels attributable to the operative stress and failing kidney function in acute uremia.