Three groups of 30 children each will be studied: Group 1, children with asthma and sickle cell disease; Group 2, children with sickle cell disease but without asthma; Group 3, control group of 30 African American children with asthma but without sickle cell disease ; Group 4, healthy control group of 25 African American children with no chronic disease. All children are seen at Nemours Children's Clinics in Jacksonville FL, Orlando FL, or Wilmington DE.