We describe 3 patients with metastatic medullary carcinoma of the thyroid who were treated with doxorubicin hydrochloride (Adriamycin). Serum calcitonin was measured before and after doxorubicin therapy. Doxorubicin failed to arrest the progression of the disease in any of the patients. Although serum calcitonin levels dropped in 1 patient during therapy, they remained markedly elevated in all 3 patients. From the present series it appears that medullary thyroid carcinoma often does not have a response to doxorubicin.