To test the effect of the pituitary-adrenocortical system on pyruvic acid metabolism, blood and urine pyruvic acid levels were detd. in patients during treatment with ACTH and cortisone. In most patients the level increased, while there was a significant decrease in the eosinophils. It was suggested that a rise in blood pyruvic acid after the admn. of ACTH may be a sign of functional integrity of the adrenal cortex.