Purpose: To identify racial/ethnic differences in retention of older adults at 3 levels of participation in a prospective observational study: telephone, in-home assessments, and home visits followed by blood draws.Design and Methods: A prospective study of 1,000 community-dwelling Medicare beneficiaries aged 65 years and older included a baseline in-home assessment and telephone follow-up calls at 6-month intervals; at 4 years, participants were asked to complete an additional in-home assessment and have blood drawn.Results: After 4 years, 21.7% died and 0.7% withdrew, leaving 776 participants eligible for follow-up (49% African American; 46% male; 51% rural). Retention for telephone follow-up was 94.5% (N = 733/776); 624/733 (85.1%) had home interviews, and 408/624 (65.4%) had a nurse come to the home for the blood draw. African American race was an independent predictor of participation in in-home assessments, but African American race and rural residence were independent predictors of not participating in a blood draw.Implications: Recruitment efforts designed to demonstrate respect for all research participants, home visits, and telephone follow-up interviews facilitate high retention rates for both African American and White older adults; however, additional efforts are required to enhance participation of African American and rural participants in research requiring blood draws. © The Author 2011. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved.