Subjects have a form of sickle cell disease, called hemoglobin SC disease. This results in abnormally shaped red blood cells that get 'stuck' in blood vessels and then results in episodes of severe pain (pain crises). Patients with the more common form of sickle cell disease, called hemoglobin SS disease, also suffer from pain crises. Treatment with the drug hydroxyurea is available to help prevent the pain crises in hemoglobin SS disease, but there is no good treatment to help prevent the pain crises in hemoglobin SC disease.