A randomized clinical trial designed to assess the therapeutic value of ascorbic acid in treatment of early onset cystinosis was conducted. Patients giving informed consent were randomized to either a liquid or tablet form of ascorbic acid or placebo. The ascorbic acid was prescribed at a dose of 200 mg/kg/day. The preparations of ascorbic acid and placebo were identical in physical characteristics so that neither the physician nor the patient knew which treatment was being administered. In November 1977, the Data Monitoring Committee stopped the trial, since there was no evidence that vitamin C was effective, and there was some suggestion that it might be detrimental. At the time of discontinuation, 32 patients in each group had reported exams. The total follow-up experience in both groups represented approximately 104 person-years. Patients on vitamin C showed greater rises in serum creatinine; of eleven children who required dialysis, transplant or died, eight were taking vitamin C.