A 33 year old woman was diagnosed at surgery with a PRL-producing pitu
itary adenoma containing spherical amyloid. Circulating PRL in this pa
tient 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. Immunohis
tochemical staining of the pituitary amyloid deposits was negative for
calcitonin gene-related peptide and islet-amyloid polypeptide. Pituit
ary amyloid may be different from amyloid in other endocrine tissues.