The National Marrow Donor Program (NMDP) was established in 1987 in order to (1) create a registry of volunteer, prospectively tissue-typed, unrelated bone marrow donors, (2) facilitate the performance of matched unrelated donor marrow transplants through a coordinated circuit of Donor Centers, Collection Centers and Transplant Centers throughout the United States, and (3) evaluate the outcome of such transplants and identify future areas of research in the field of unrelated donor marrow transplants. The NIH Marrow Donor Center, a participant in the NMDP, is currently the second largest hospital-based Donor Center in the nation, with approximately 55,900 active donors on its registry. 402 NIH unrelated donors to date have undergone 429 marrow or blood stem cell harvest for an NMDP recipient, and the current rate of such harvests is three per month. Once an HLA-matched donor in the NIH Donor Center registry is identified through the NMDP computer network, the donor must undergo a medical evaluation to determine suitability for marrow harvest. This evaluation consists of a medical history, a physical examination, routine blood work, EKG, chest x-ray, and urinalysis, and generally takes 4 to 6 weeks. A "third party" non-NIH physician usually performs the evaluation, with the costs reimbursed by the NMDP. Occasionally, an expedited evaluation of an unrelated donor must be performed, due to the urgency of the need for a transplant in the recipient, and there is insufficient time to accomplish this work-up using the routine "third-party" physician's office mechanism. This protocol shall provide a means by which prospective NIH unrelated marrow donors participating in the NMDP program can undergo an expedited medical evaluation to determine suitability for marrow donation. It is expected that not more than 5 to 10 donors per year shall require such expedited evaluation.