 The investigators will examine the patients medical records to find out how many times they have been admitted to the hospital for sickle cell crisis in the last 12 months. The investigators will also obtain information on the following: their age, their sex, whether they are taking hydroxyurea or Penicillin, when they last had a transfusion or exchange transfusion therapy and painful crisis needing hospital admission, whether they have received any antibiotics other than Penicillin in the last 4 weeks, and whether they are experiencing a painful crisis at the time that they enter the study. The investigators will obtain, from their previous laboratory results, their levels of hemoglobin F and markers of inflammation. The investigators will check their hemoglobin F level if they have not already had this tested. 