The critical event leading to serious morbidity in sickle cell disease is polymerization of the abnormal hemoglobin to form fibers that stiffen and distort red blood cells and consequently, cause vaso-occlusion in the small vessels of the tissues. Currently, hydroxyurea is the only approved drug for treating sickle cell disease, but is only partially effective. This protocol seeks to identify by high sensitivity in vitro screening methods additional compounds that inhibit sickling. Subjects with sickle cell trait or disease and normal volunteers will be asked to donate blood samples for studies to verify their hemoglobinopathies and then periodically donate small volume samples of fresh blood for use in ongoing high throughput screening tests to identify potentially clinically useful anti-sickling drugs.