The expression of amylase in various histological types of thyroid cancer was studied by an immunohistochemical technique, using a polyclonal antiamylase antiserum and two monoclonal antibodies specific for salivary and pancreatic-type amylases, respectively. Amylase was expressed in 21 of 24 (88%) thyroid cancers by polyclonal antiserum analysis. Analysis by monoclonal antibodies, however, showed that only 13 (54%) cases and three (13%) cases contained salivary-type and pancreatic-type amylases, respectively. Moreover, immunoreactivity for pancreatic-type amylase was detected only in medullary carcinoma; other histological types were positive for salivary-type amylase. These results show that thyroid cancer frequently expresses amylase, and suggest that the differences between amylase isoenzymes in thyroid cancer may correlate with those found between cellular origin of tumour.