Tumor lysis syndrome is a life-threatening complication of chemotherapy for patients with leukemia and large tumors with a high proliferative index, such as Burkitt's lymphoma. The syndrome is characterized by hyperkalemia, hyperphosphatemia, hypocalcemia, and hyperuricemia. The standard of care for hyperuricemia consists of hydration with or without alkalinization and administration of allopurinol. When treated in this manner, patients often experience persistent hyperuricemia that lasts several days after the start of antineoplastic therapy; sometimes they develop uric acid nephropathy as a consequence. Rasburicase, a recombinant urate oxidase enzyme, quickly removes large amounts of uric acid from plasma. The drug is approved by the United States Food and Drug Administration for management of elevated plasma uric acid levels in pediatric patients with leukemia, lymphoma, or solid tumor malignancies who are receiving chemotherapy. We undertook a retrospective review of adult patients treated with a single dose of rasburicase 6 mg for hyperuricemia associated with malignancy. Ten patients received one 6-mg dose of rasburicase, and one patient received two 6-mg doses as an adjuvant therapy to normalize uric acid levels. In most of the patients, a single 6-mg dose of rasburicase was effective in correcting uric acid levels in the typical time between diagnosis and start of antineoplastic therapy.