Parathyroid carcinoma is a rare cause of hyperparathyroidism. Cure results from successful en bloc resection. However, because of its rarity, the malignant nature may not be appreciated at the initial operative procedure and as a result, definitive resection may not be accomplished. However, even with extensive en bloc resections, local recurrences do occur and patients die of metabolic derangements associated with hypercalcemia. Thus in addition to operative intervention, palliative chemotherapy may be required to control the hypercalcemia. Radiotherapy has been unsuccessful. A single case of nonfunctioning parathyroid carcinoma responding to treatment with methotrexate, Adriamycin, cyclophosphamide, and CCNU has been reported. We report a case of recurrent functioning parathyroid carcinoma treated with dacarbazine (DTIC) in which biochemical and pathologic evidence of at least a partial response was seen. The patient, a 33-year-old woman, had undergone five previous neck explorations during a 26-month period for aggressive locally recurrent disease. Before DTIC therapy the intact parathyroid hormone (PTH) level was 1032 pg Eq/ml (normal 163 to 347 pg Eq/ml) and the serum calcium level was 16.8 mg/dl (normal 8.8 to 10.0 mg/dl). After a course of DTIC there was a marked improvement in her clinical status and biochemical parameters (intact PTH 545 pg Eq/ml; serum calcium 11.8 mg/dl). For 2 months her condition stabilized, with PTH levels between 700 and 760 pg Eq/ml and serum calcium levels between 10.2 and 16.0 mg/dl. With a slowly progressive rise in biochemical parameters a second course of DTIC was initiated and a marked drop in serum calcium levels (5.7 mg/dl) occurred, but PTH levels remained unchanged. A progressive course of septicemia, malnutrition, and disseminated intravascular clotting ultimately lead to her death 4 weeks later. At autopsy examination the tumor was confined to the neck. Grossly and microscopically there was extensive central as well as peripheral necrosis of the tumor, which was thought to be the result of the cytotoxic effect of DTIC. From this experience and because of the grim prognosis in patients with recurring parathyroid carcinoma, it may be that aggressive use of chemotherapy with DTIC early in the course of treatment should be considered.