A 60-year-old Japanese woman who presented with right nasal congestion and high fever was admitted to our hospital in March 1999. She was diagnosed with nasal NK/T-cell lymphoma clinical stage IVB. Because her NK/T-cell lymphoma was highly aggressive and chemo-resistant, she underwent autologous peripheral blood stem cell transplantation (PBSCT). The patient received a pretransplantation conditioning regimen of ranimustine, etoposide, carboplatin, and cyclophosphamide. On July 29, 1999, 1.0 x 10(6)/kg CD34+ cells were infused. The patient achieved first complete remission. In January 2000, NK/T-cell lymphoma relapsed in the skin and fever developed. CHOP (cyclophosphamide, vincristine, doxorubicin, and prednisolone) was administered, resulting in partial regression of the skin lesions, but fever persisted. L-asparaginase (L-Asp) at a dose of 6,000 U/m2 per day was administered for 7 days, resulting in the complete disappearance of the skin lesions and resolution of the fever. The patient has been in second complete remission for more than 18 months since the completion of L-Asp treatment (as of July 2001). The effect of L-Asp in this patient was dramatic. Several cases have been reported describing the effectiveness of L-Asp in patients with nasal lymphoma and cutaneous T-cell lymphoma. A front-line chemotherapy regimen containing L-Asp for NK/T-cell lymphoma may warrant further evaluation.