L-asparaginase (L-Asp) is an important reagent for acute lymphoblastic leukemia because asparagine is required for the malignant growth of tumor cells, especially lymphoblastic leukemia cells. An allergic response to L-Asp is not unusual because L-Asp is derived from Escherichia coli and is often recognized as a foreign protein. The hypersensitivity induced by L-Asp is of the immediate type in most cases. We report on a 5-year-old girl who was hospitalized for precursor T-cell lymphoblastic leukemia. She was treated according to a Tokyo Children's Cancer Study Group protocol (TCCSG ALL L09-1603 HEX/BFM). During the intensification phase, blisters with erythema developed on the arm proximal to the catheter insertion site owing to a delayed-type hypersensitivity reaction caused by intravenous L-Asp administration. She was treated with additional methylprednisolone, tapered dexamethasone, and an antihistamine for the allergic reaction. No asparaginases other than E. coli L-Asp have been approved for use in Japan. Other asparaginases, such as polyethylene glycol L-Asp and Erwinia L-Asp should be quickly approved for use as alternative chemotherapy reagents in Japan.