OUTLINE: Peripheral blood samples are collected from donors prior to stem cell mobilization and from patients prior to starting preparative regimen. Samples are studied by single nucleotide polymorphism (SNP) analysis, SNP array, proteomic analysis, gene expression, and other immunological laboratory methods. Blood, urine, and tissue samples are preserved for future studies. Extra skin biopsies and gastrointestinal biopsies are performed at diagnosis of graft-vs-host disease and preserved in a tissue bank for flow cytometric studies.