Hematopoietic stem-cell transplants (HSCT) are commonly used in the treatment of blood and lymphoid cancers. In an allogeneic transplant, the transplanted cells come from a donor. After such an allogeneic HSCT, patients must take a variety of medications, to prevent rejection of the transplanted cells and to fend off infections due to severe immunosuppression. This medication regime is complex and requires rigorous adherence, usually extending for at least 6 months after transplant. Clinical data suggest that medication nonadherence places patients at risk for increased morbidity and mortality, requiring hospital readmissions with increased medical and economic costs. No systematic studies are available on HSCT patients' medication adherence after transplant. Predictors of nonadherence in HSCT patients are not well understood. Possible risk factors, such as history of nonadherence, lack of social support, and depression, are more prevalent among low-income minority groups for which post- transplant mortality and morbidity are higher than among majority groups. In sum, there is clearly a need to study (1) medication adherence, (2) the link between adherence and transplant outcomes, and (3) predictors of adherence and nonadherence in HSCT patients including low-income and minority patients. To address this scientific need, the study will assess medication adherence in 40 allogeneic HSCT patients (including 20 minority patients) during the first six months after treatment. In addition, the study will use a multi-method approach to examine predictors and processes related to medication adherence through qualitative patient interviews and standard questionnaires. The proposed research is innovative in three distinct ways: 1) It will address the understudied problem of medication adherence in HSCT patients. 2) It will use daily electronic monitoring, drug plasma levels, and self-report to assess adherence with a complex medication regime. 3) It will apply an established empirically supported theory of adherence model (the Information-Motivation-Behavioral Skills Model) to this population. We anticipate that the proposed study will identify strategies to promote adherence in patients with complex medication regimes who are at risk for nonadherence, including low-income and minority patients.