Optimal salvage chemotherapy has not been established for lymphoid malignancy, which is refractory to the conventional cyclophosphamide, doxorubicin, vincristine, and prednisone regimen. To explore an effective regimen, we conducted a phase I pilot study of combination chemotherapy with methotrexate, ifosfamide, l-asparaginase and dexamethasone (MILD), which are unaffected by MDR1-encoded P-glycoprotein. A total of 18 patients with lethal lymphoid malignancy were enrolled over a 2-yr period. The median age was 63 yr. Eleven patients had T/NK-cell malignancies, six had B-cell malignancies, and one was diagnosed with a blastic plasmacytoid dendritic cell neoplasm. Patients aged >/=60 and <60 yr were planned to receive a set of starting doses of methotrexate and ifosfamide, which should induce myelosuppression. Eleven patients completed two courses of MILD therapy. Treatment-related death because of systemic mucormycosis was observed in one patient. Major treatment-related adverse events were grade 3 or more hematologic toxicities, which included lymphopenia corresponding to dose-limiting toxicity. The most common grade 3 non-hematologic toxicity was febrile neutropenia. Of the 14 evaluated patients, three achieved a complete response, and four showed a partial response. The overall response rate was 57%. It was very interesting that all of seven responders had T/NK-cell malignancies. MILD therapy was feasible and presented acceptable toxicity in patients with refractory or lethal lymphoid malignancies. The efficacy for T/NK-cell malignancies should be further evaluated.