A Merkel cell carcinoma of the mandibular area in a 78-year-old woman was treated successfully by direct intratumoral administration of recombinant human tumor necrosis factor. The patient received 2.5 x 10(5) U/d of recombinant human tumor necrosis factor every other day. A total of six injections (total dose, 1.5 x 10(6) U, 0.52 mg of protein) were administered over a period of 12 days. Soon after the therapy ended, the lesion softened and decreased in size. After 1 month, only erythema was visible. The lesion had completely disappeared clinically and histologically 5 months after the local injection of recombinant human tumor necrosis factor. Neither recurrence nor metastasis has been observed for at least 12 months following the treatment. Recombinant human tumor necrosis factor is suggested to be effective for the treatment of Merkel cell carcinoma.