THE ASSOCIATION OF Cushing's syndrome and carcinoma of the lung has occurred with sufficient frequency to suggest more than a coincidental relationship. The idea that the tumor might, in some manner, stimulate the pituitary to secrete ACTH has been suggested by the finding of elevated plasma ACTH levels in several patients.1,2However, this finding is also consistent with the concept that the neoplasm itself secretes a corticotropic substance that acts directly on the adrenal glands. The following case is that of a patient with fulminating Cushing's syndrome and an oat cell carcinoma of the lung. Endocrinologic studies performed during life, postmortem bioassay of the tissue obtained from the anterior pituitary, and the neoplasm for corticotropic activity, form the basis of this report. Report of a Case A 49-yr-old male entered the Boston Veterans Administration Hospital on June 16, 1961, with the chief complaint of swelling of the face