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Background: Rasburicase is a recombinant urate oxidase enzyme that converts uric acid to allantoin (an inactive and soluble metabolite that is readily excreted in urine). It is used for the management of tumor lysis syndrome (TLS) in cancer patients receiving chemotherapy. Although rasburicase is a generally safe and effective treatment, it can be associated with the rare and potentially severe complication of methemoglobinemia. Here, we report a case of rasburicase-induced methemoglobinemia in a patient who was diagnosed with aggressive non-Hodgkin's lymphoma., Case Report: A 74-year-old man with aggressive non-Hodgkin's lymphoma was admitted for initiation of chemotherapy. Upon admission, the patient was found to have hyperkalemia, hyperuricemia, hyperphosphatemia, elevated LDH levels, and acute renal failure. As a result, he was diagnosed with TLS. Rasburicase 6 mg was administered intravenously over a period of 30 min to treat TLS. Later, methemoglobinemia developed, with requirements for oxygen supplementation. Multiple units of packed red blood cells were transfused for recurrent significant anemia secondary to his cancer co-morbidity. The patient was tested for glucose-6 phosphate dehydrogenase (G6PD) deficiency, which returned negative; therefore, methylene blue was considered. After transfusion, the methemoglobin level normalized over the course of a few days, and the oxygen saturation improved without the use of methylene blue. However, during his hospitalization, the patient also developed a pulmonary embolism and had evidence of acute coronary syndrome. Later, the patient died of multiple complications related to his cancer co-morbidity on day 12 of admission., Conclusions: Blood transfusion and supplemental oxygen, without the use of methylene blue, may be an appropriate therapeutic alternative in rasburicase-induced methemoglobinemia treatment.