A 33 year old woman was diagnosed at surgery with a PRL-producing pituitary adenoma containing spherical amyloid. Circulating PRL in this patient was immunologically and chromatographically similar to classical 20,000-dalton PRL. PRL staining within the tumor was confined to the adenoma cells and was not found within the amyloid deposits. Immunohistochemical staining of the pituitary amyloid deposits was negative for calcitonin gene-related peptide and islet-amyloid polypeptide. Pituitary amyloid may be different from amyloid in other endocrine tissues.