Patients 18 years of age and older with severe thalassemia major may be eligible for this study. Before beginning treatment, candidates will have a medical history and physical examination, blood tests, chest X-ray, electrocardiogram (EKG), bone marrow biopsy (removal of a small sample of bone marrow from the hip for microscopic examination) and whole-body magnetic resonance imaging (MRI). For the biopsy, the area of the hip is anesthetized and a special needle is inserted to draw bone marrow from the hipbone. For the MRI scan, a strong magnetic field is used to produce images that will identify sites where the body is making red blood cells. During this procedure, the patient lies on a table in a narrow cylinder containing a magnetic field. Earplugs are placed in the ears to muffle the loud thumping sounds the machine makes when the magnetic fields are being switched.