A 20-year-old woman had a sporadic case of medullary thyroid carcinoma (MTC) metastatic to the lungs. After a transient response to streptozotocin and doxorubicin, new subcutaneous lesions appeared on the left chest wall and there was progression of pulmonary disease. Because MTC is one of the amine precursor uptake and decarboxylation (APUD) tumors, treatment was undertaken with agents active in these diseases. Dacarbazine and 5-fluorouracil, given daily for 5 days every 4 weeks, resulted in complete resolution of pulmonary and subcutaneous lesions and a sharp decrease in tumor marker levels that lasted 10 months. Recurrence of the pulmonary disease lead to her death 21 months after presentation. Thus, the chemo-responsiveness of MTC may be akin to that of other APUD carcinomas (APUDomas) and treatment of metastatic MTC and other APUDomas with the combination of dacarbazine and 5-fluorouracil appears to merit further study.