Propanolol is a beta blocker which has been found to inhibit the ability of epinephrine to upregulate sickle red cell adhesion to laminin and endothelial cells in vitro. The purpose of this pilot study is to administer one dose of propanolol to children with sickle cell disease and to measure pre and post dose red cell adhesion. The hypothesis is that a single dose of propanolol will decrease red cell adhesion to laminin and endothelial cells as compared to baseline.