The hydrocortisone and ACTH blood levels, 17-hydroxycorticosteroids urine excretion and suprarenal function stimulation with Synacthen were studied in 22 patients with chronic obstructive pulmonary disease and 12 healthy persons as controls. The results show the presence of reliably higher hydrocortisone and 17-hydroxycorticosteroids levels in patients with low partial oxygen pressure as well as a higher ACTH plasma level and a strong Synacthen stimulation. After a comprehensive treatment including oxygen therapy the blood concentrations of hydrocortisone, ACTH, 17-hydroxycorticosteroids fell to levels found in healthy persons. The study shows that hypoxemia stimulates the suprarenal-cortex secretion.