Patients with renal insufficiency have been identified in four renal outpatient clinics, i.e., the Brady Green, Audie L. Murphy Memorial Veterans Hospital, Brooke Army Medical Center, and Wilford Hall USAF Medical Center. A total of 106 subjects have been identified at this time as potentially suitable for study. Patient counseling, examination and GFR measurements will be undertaken in the Special Diagnostic Treatment Unit/Frederic C. Bartter Clinical Research Unit (SDTU/CRU) located on the 7th floor of the ALMMVH. An office is available for the computer, file cabinets, and the Data Entry Clerk/Secretary. Adjacent space will be made available for the Study Coordinator, Dietitians, etc.