To the Editor.— We feel compelled to report the complications of high-dose vitamin C infusion in patients with renal insufficiency. Vitamin C, one of whose main metabolites is oxalate, can produce permanent renal failure in patients with preexisting renal insufficiency. Report of a Case.— A 70-year-old man with documented renal insufficiency came to a "chelation therapy" center for treatment of claudication. Previous testing (one day before) showed the serum creatinine level to be 5.0 mg/dL. An estimated creatinine clearance was 19 mL/min. The serum hematocrit value was 29.4%. To be prepared for chelation—the intravenous (IV) administration of edetic acid—the patient was given 2.5 g of vitamin C in 500 mL of solution of 5% dextrose in water for five hours. The patient tolerated the infusion well; however, 12 hours later he experienced severe lancinating bilateral flank pain, passed 3 mL of hematuria, and became anuric. The patient was transferred to