Patients will take pirfenidone by mouth 3 times a day for 12 months. Blood and urine will be tested once a month, either at NIH or by the patient's local kidney specialist. They will collect two 24-hour urine samples at the beginning of the treatment period, at 2-month intervals throughout the study, and at a 6-month follow-up. Patients will also be asked to give three to five tubes of blood and urine samples for analysis during the study.