The development of protocols to induce a state of durable mixed allogeneic hematopoietic chimerism to confer robust donor-specific transplant tolerance has been a major focus of the transplant community for the past decade. High levels of mixed allogeneic hematopoietic chimerism across a full major histocompatibility complex (MHC) barrier can be achieved by total myeloablation and transfusion of host and donor bone-marrow cells (1) or, as shown more recently, can be achieved with nonmyeloablative preconditioning regimes in combination with donor bone-marrow transfusions (2-4) or transfusion of purified hematopoietic stem cells (HSC) (5-7). Here we illustrate useful experimental techniques for the study of hematopoietic chimerism in rodents by describing a system in which chimerism can be induced using nonmyeloablative conditioning, short-term costimulation blockade, and transplantation of purified or cultured hematopoietic stem cells.