This study will collect representative blood samples from healthy children and adults and from children and adults who have unique red blood cell features that are related to sickle cell disease. Sickle cell disease is a blood disease that limits the ability of red blood cells to carry oxygen throughout the body. The purpose of the study is to collect a variety of blood samples that may then be used to investigate advances and potential new drug treatments for sickle cell disease. Volunteers must be at least 18 years of old. Samples will be taken both from healthy volunteers and from volunteers who have unique red blood cell features that are related to sickle cell disease. Candidates will be screened with a medical history. During the study, participants will undergo a one- to two-hour outpatient procedure at the National Institutes of Health Clinical Center. Once researchers have explained the study and obtained the participant s consent, participants will donate 8 cc (approximately 2 teaspoons) of blood. Because repeat testing helps researchers validate study findings, participants who have the unique red blood cell features mentioned above may also be asked if they are willing to return and donate another 2 cc to 8 cc of blood for additional studies. The amount of blood drawn will not exceed 50 ml with any eight-week period for adults or 7 cc within any six-week period for children.