Patients with homozygous SCD or other sickling disorders (e.g., B(0) Thalassemia/Sickle) who are 18 years of age or greater will be eligible for treatment. Patients currently being followed on an NIH study or at Howard University on stable doses of hydroxyurea are also eligible. A total of 60 patients will be recruited to the study, with the recognition from our earlier studies of a failure-to-complete rate approaching 50%.