A 47-yr-old woman with severe Cushing's syndrome had a bronchial carcinoid secreting ACTH and corticotropin-releasing hormone (CRH) and associated pituitary corticotroph hyperplasia. While the clinical picture was consistent with the ectopic ACTH syndrome, the biochemical pattern was that of pituitary ACTH-dependent hypercortisolism. Both plasma ACTH and CRH levels were high. However, while plasma ACTH increased during metyrapone administration and decreased during administration of high dose of dexamethasone, plasma CRH levels did not change, suggesting a direct pituitary response to these testing maneuvers. Immunoperoxidase staining of the tumor tissue confirmed the presence of ACTH and CRH, and the finding of an ACTH and a CRH concentration gradient across the tumor bed indicated that the tumor was actively secreting these two hormones. Cytochemical heterogeneity was seen in the tumor, in which two distinct populations of cells, one secreting ACTH and beta-endorphin and the other secreting CRH, were identified. This patient, thus, had an unusual syndrome of ectopic ACTH and ectopic CRH secretion.