The recombinant urate oxidase, rasburicase (Elitek, Sanofi-Synthelabo, Inc.), has recently received regulatory approval for the prevention and treatment of hyperuricemia in children with leukemia, lymphoma, and solid tumors. Prior to approval, 682 children and 387 adults in the US and Canada received rasburicase on compassionate-use basis. Uric acid concentration declined rapidly in both adult and pediatric patients after rasburicase treatment. Similar responses were observed in patients treated with subsequent courses. Possible drug-related adverse events, including allergic reactions, were uncommon. These data confirm that rasburicase is effective and safe for the treatment and prophylaxis of children and adults with malignancy-associated hyperuricemia.