PIP: Pituitary function was studied before and after surgery in 1 patient who underwent chryohypophysectomy and 5 patients who underwent transsphenoidal excision hypophysectomy for metastatic breast cancer ablation therapy. Changes in serum luteinizing hormone, follicle stimulating hormone, growth hormone, thyrotropin stimulating hormone, pituitary prolactin (PRL), and steroid hormone levels of estrone, estradiol, testosterone, and rostenedione, and dehydroepiandrosterone levels were determined. All of the above were assessed before and from 6 weeks to 10 months after hypophysectomy. Pituitary hormone release in response to sequential stimuli of arginine infusion, thyrotropic releasing factor (TRF), and luteinizing hormone-releaseing factor was analyzed. In 3 patients, hypophysectomy was considered incomplete because of the presence of measurable amounts of circulating pituitary hormones and their release in response to stimuli, although all levels except PRL were markedly reduced. In 3 patients, hypophysectomy was considered nearly complete. Basal PRL levels remained unchanged whether the procedure was considered complete or not. PRL release was absent in response to TRF or arginine stimulation in 4 patients with substantial residual pituitary function. Hypophysectomy was followed by a marked reduction in circulating levels of estrogens and androgens. The assessment of quantitative release of pituitary hormones in response to stimuli is an improved direct measure of residual functioning pituitary tissue.