Patients 18 years of age and older with sickle cell anemia and kidney disease or pulmonary hypertension, or both, may be eligible for this study. Candidates are screened with a medical history, physical examination, blood tests, a 6-minute walk test (test to see how far the subject can walk in 6 minutes), and echocardiogram (ultrasound of the heart to measure blood pressure in the lungs).