Plasma ACTH was determined by a modification of the method of Lipscomb and Nelson (femoral method) but, in some cases, test materials were injected into the aorta (aortic method).1) After the oral administration of SU-4885, 3.0 g. per one day, plasma ACTH rose to a mean±standard error (S.E.), 1.6±0.4 mU/100 ml, ranging from 0.6 to 4.0 mU per 100 ml. in 9 endocrinologically normal subjects. In 5 patients after long-term steroid treatments plasma ACTH was not detectable except in one case. All 5 patients with anorexia nervosa had distinctly elevated ACTH levels after the administration of SU-4885. Two of 5 patients with anorexia nervosa showed more than normal rises both in plasma ACTH and in urinary 17-OHCS excretion. In 2 patients with Cushing's syndrome due to adrenal cortical hyperplasia no detectable ACTH in plasma was found, whereas one patient with Cushing's syndrome due to adrenal cortical adenoma had an elevated ACTH level after the administration of SU-4885, who showed good response to ACTH. However, no ACTH was detected in one unilaterally adrenalectomized patient for a adrenal cortical adenoma, even 2 years after an operation. Elevated ACTH levels were also noted in one patient with liver cirrhosis and one patient with Laurence-Moon-Biedle's syndrome. Generally, the elevated plasma ACTH levels were associated with high values of urinary 17-OHCS excretion, although there were several exceptional cases.2) In 8 of 13 patients undergoing a major operation, such as laparotomy or thoracotomy, plasmas obtained one hour after the incision were found to have elevated ACTH levels ranging from 0.6 to 19.1 mU per 100 ml of plasma, which returned toward nondetectable levels within 24 hours postoperatively with the exception of one case. It was noted that increases in plasma ACTH occurred coincident with elevations in plasma cortisol when both were measured simultaneously in 6 cases. Plasma from two schizophrenic patients receiving electroconvulsive therapy was found to contain elevated ACTH levels.3) The normal diurnal rhythm of plasma ACTH, that is, the rise in the early morning and the decline in the evening was noted in normal subjects, whereas it was absent in patients with Cushing's syndrome due to adrenal cortical hyperplasia. On the other hand, 4 patients : wiht adrenogenital syndrome and 10 patients with Addison's disease maintained the diurnal variation, showing greater differences than normal subjects between plasma ACTH levels in the early morning and those in the evening.