Upon admission, the patients will be physically examined and started on a special diet that will continue throughout the study. During the first four days of the study, the weight, heart rate and blood pressure of the patients will be measured every morning and 24-hour urine will be collected. On day 5, intravenous lines will be inserted in the patient's arms. One line will be used to draw blood samples and the other line will be used to infuse medications. Blood samples will be taken to measure liver and kidney function, nitric oxide, and other hormones that participate in the regulation of body fluids and blood pressure. Inulin and paraaminohippurate infusions (substances used routinely in the study of kidney function) will be started and blood and urine samples will then be taken at periodic intervals. Ninety minutes after the initiation of inulin and PAH infusions, L-NMMA (an investigational drug expected to increase the blood pressure and improve the kidney functions) will be infused. Blood and urine samples will be collected every 30 minutes. These procedures will take 4 hours. A total amount of about 10 tablespoons of blood will be drawn during the study. The patients will be discharged from the GCRC the next morning and restarted on their regular medications.