It is now almost 2 decades after the first successful human marrow transplants from HLA-identical siblings for the treatment of life-threatening hematologic diseases. Results have improved, especially for patients transplanted earlier in the course of disease. However, major problems remain in supporting patients through the transplant. More effective and less toxic conditioning regimens are needed. Acceleration of hematopoietic and immunologic reconstitution by use of various cytokines holds promise for decreasing infectious morbidity and mortality. Improved regimens to control acute and chronic GVHD and prevent opportunistic infections will play a major role in the advancement of supportive care of the marrow transplant recipient.