Patients aged 10 to 80 years who are scheduled to undergo bone marrow transplant at the NIH Clinical Center as part of an NIH protocol may be eligible for this 2-phase study. In phase 1, patients will have blood drawn for both RT PCR and antigenemia testing once before the bone marrow transplantation and then weekly for the first 100 days after the transplant. During Phase 2-which begins immediately after the end of phase 1 and continues for one year after the transplant-blood samples for both tests will be drawn up to once a week. The samples for both tests will be collected at the same time and will be taken through a catheter (a thin flexible tube inserted into a vein) that has already been placed for the transplant study. RT PCR testing will require an extra 5 milliliters (1 teaspoon) above what is needed for antigenemia testing, amounting to a maximum of about one-half pint extra over the course of the 1-year study.