In the quest for a better evaluation of the indications for the therapeutic use of corticotropin (ACTH) and of adrenocortical steroids (cortisone, etc.) in surgical diseases, more about the nature and degree of the adrenocortical response to operation must be known. To this end, investigators have used a number of methods, including measurements of certain adrenocortical steroids and their metabolic products excreted in the urine, the eosinophile count of the peripheral blood, and the uric acid-creatinine ratio in the urine. The present report deals with a study of adrenocortical function based on quantitative determinations in the peripheral blood at intervals before and after operation of two groups of adrenocortical steroids. The two groups are (a) 17-hydroxycorticosteroids (17-OHCS), which have in common both an alpha ketol and a hydroxy group in the 17 position and include, among others, compound E (cortisone) and compound F, and (b) 17-desoxycorticosteroids (17-desoxy CS), which differ