This study was performed to evaluate hypothalamic-pituitary hormone regulation in patients with familial amyloidotic polyneuropathy. Twenty-two patients without clinically overt endocrinological dysfunction were studied. A thyrotropin-releasing hormone test revealed abnormal growth hormone regulation in 9 of 17 (53%) patients, and abnormal prolactin regulation in 9 of 18 (50%) patients. Abnormalities in either growth hormone or prolactin regulation were found in 12 of 17 (71%) patients. Serum somatomedin C levels were normal in all 22 patients. In 3 of 18 (17%) patients the plasma arginine vasopressin levels were low relative to the serum osmolality levels. Thus abnormalities in hypothalamic-pituitary hormone regulation may be common in familial amyloidotic polyneuropathy.