To the editor: Recent successful results using "high-dose" methotrexate with citrovorum factor rescue in the treatment of head and neck carcinoma and osteogenic sarcoma have led to more widespread use of this therapy in the treatment of these and other tumors. A major complication of high-dose methotrexate therapy has been impairment of renal function with rising serum creatinine levels and lowered creatinine clearance. This toxicity has led to delayed renal excretion of methotrexate, which subsequently produces myelosuppression in spite of standard citrovorum factor rescue (1). Removal of methotrexate from patients with impaired renal function would be beneficial in decreasing the