SummaryExperiment and pathology have shown that cortisone treatment induces anterior pituitary inhibition and adrenocortical involution.The clinical and biological manifestations of this phenomenon have been searched for in patients presenting hyperadrenocorticism (adrenogenital, Cushing or Achard-Thiers syndromes), also in cases of bronchial asthma, periarteritis nodosa or rheumatoid arthritis treated with cortisone.Adrenocortical activity was shown to be inhibited in each of its aspects. A lowering of blood pressure in 3 patients presenting hyperadrenocorticism and hypertension indicates the inhibiting effect of hormone therapy on corti- coid secretion regulating scdium metabolism. Inhibition of the hyperglycemic function of the adrenal cortex is demonstrated by a reduction of blood glucose and by an increase of glucose tolerance and insulin sensitivity.Regression of virilism and decrease in 17-k.s. excretion emphasize the effect on androgenic function.Inhibition of the pituitary-adrenocortical axis sometimes leads to fatal accidents; one case is described. The paradoxal improvement noted in some cases of steroid diabetes treated with cortisone suggests that such a treatment could-be used to evaluate the role played by enhanced adrenocortical secretion in the genesis of some diabetic states.