This study will evaluate the safety of eptifibatide in sickle cell patients and how well it works during the course of painful crises. The overall hypothesis that we seek to test is that increased platelet activation and the resultant inflammatory responses are important contributors to the problems of sickle cell disease. Sickle cell disease has been referred to both as a condition associated with increased risk of blood clots and increased inflammation. A painful crisis represents the most common cli nical problem in sickle cell disease, but the treatment of these crises remains inadequate.