This study was undertaken to determine if the adrenocortical hormone was concerned on erythropoietic function, especially on the production of erythropoietin in the kidney. Erythropoietin titers in plasma measured in each group of mice: 1) hypertransfused mice treated with the plasma of rats pretreated with hydrocortisone, dexamethasone, fludrocortisone and DOCA 2) hypertransfused mice treated with the plasma of the rat pretreated with aldosterone antagonist and adrenocortical hormone concomitantly. Erythropoietin level in plasma were measured by the modification of DeGowin s method. The results of the experiment were summerised as follows: 1) No significant changes of erythropoietin titers were observed in hypertransfused mice treated with the plasma of rats pretreated with hyrocortisone and dexamethasone respectively. 2) Erythropoietin titers increased significantly in hypertransfused mice treated with the plasma of rats pretreated with fludrocortisone and DOCA respectively, compared with control. 3) No significant changes of erythropoietin titers were observed in hypertransfused mice treated with the plasma of rats pretreated with spironolactone and triamterene respectively, compared with control. 4) Erythropoietin titers slightly increased in hypertransfused mice treated with the plasma of rats pretreated with spironolactone or triamterene, and fludrocortisone concomitantly and also with spirolactone or triamterene and DOCA.