 Healthy volunteers between 18 and 65 years of age and all patients requiring TRH evaluation of hypothalamic-pituitary-thyroid gland interaction may be eligible for this study. Patients include those with pituitary reserve, inconsistent thyroid function test, inappropriate TSH secretion, or pre- and post-operative evaluation of pituitary tumors. Normal volunteers will be screened with a medical history, physical examination, and blood tests. Women of child-bearing potential will be given a pregnancy test; pregnant and breast-feeding women may not participate. 