since the hematopoietic transplantation was performed for the first time, the importance of knowing chimerism was underlined. the present paper updates the concepts of chimerism, its classification and the different ways to determine it. the most recommended is the highly polymorphic area amplification in the dna using the polymerase chain reaction technique. this technique has allowed carrying out studies on the evolution of chimera, to relate the set level of chimerism with the graft behaviour and the graft-versus-host disease under different conditioning. it has also made it possible to early detect relapse of transplanted patients and the prompt administration of additional immunotherapy. finally, the paper presents the recommendations of the american society of blood and bone marrow transplantation for standardizing the study of chimerism in the therapy centers
