Hematopoietic stem cell (HSC) transplantation is a preferred treatment for a variety of life-threatening diseases. Because only 30% of patients needing an HSCtransplant can find a related donor, -7,000 patients are searching the National Marrow Donor Program (NMDP) registry for an unrelated donor at any given time. Although all patients may face difficulty finding an unrelated HSC donor, this problem is particularly acute for ethnic minority patients who possess less common HLA types and who encounter higher attrition rates (~50%) among registered minority donors. The reasons for higher attrition rates among minority potential donors and the experiences of minorities who actually donate have not been examined. The proposed study will examine the role of culturally-based traditions/beliefs (e.g., medical mistrust, religious beliefs) in (a) potential donors' decisions of whether or not to donate HSCs, and (b) the health experiences of unrelated donors who actually donate HSCs. The study will be conducted in collaboration with the NMDP which manages the largest registry of unrelated HSC donors in the world (> 5 million). Cross-sectional telephone interview data gatheredfrom potential donors who match a patient (n=2,400) will allow us to examine the association of cultural factors with the decision of whether to continue or opt-out of the registry. Prospective data gathered from actual donors (n=500) will allow us to examine the role of cultural variables in donors' health-related donation experiences. The specific aims of the proposal are to (1) describe a group of ethnically diverse potential and actual HSC donors along four dimensions (culturally- based, psychosocial, donation-related, and background characteristics), (2) examine the association of variables in the four dimensions with key outcomes among potential and actual donors, and (3) investigate the extent to which culturally-based characteristics account for the observed relationship between ethnicity and key study outcomes. This study overcomes limitations of previous studies by (a) investigating actual donation-related decisions rather than hypothetical willingness to donate, (b) including all 5 major U.S. ethnic groups, and (c) gathering data on the benefits and the less positive aspects of donation. Findings from this study will be relevant to retention/protection policies for all HSC donor registries, to the equitable access of minority patients to unrelated HSC donors, and to the broader role of cultural issues in organ/tissue donation.