The transplantation of bone marrow requires the recipient to create a new immune system as stem cells divide and differentiate into lymphocyte effector cells. The establishment of host immune capabilities posttransplant is critically dependent on the migration of immature and mature lymphocytes to lymph nodes, as these tissues function principally to promote lymphocyte maturation and differentiation into immunologic effectors. The first step in the directed migration of lymphocytes into lymph nodes is the attachment of the cells to lymph node high endothelial venules (HEVs), and the molecular basis of this interaction is well characterized. Experimental evidence indicates that bone marrow transplantation results in perturbations in the migration of lymphocytes to lymph nodes by affecting lymphocyte-HEV adherence: pretransplant conditioning regimens have toxic effects on HEV that decrease their capacity to support lymphocyte adherence, and the use of pharmacologic agents posttransplant may be associated with alterations in the level of expression of lymphocyte membrane adhesion proteins that mediate attachment to HEV. A greater understanding of these effects should lead to development of transplant regimens that preserve the physiologic trafficking of lymphocytes to lymph node, thereby accelerating the rate of immunologic recovery following transplant.