Literally, the ability of tissues to get along. In immunology, it means identity in all transplantation antigens . These antigens, in turn, are collectively referred to as histocompatibility antigens.

Also refers to the similarity of tissue between different individuals. The level of histocompatibility describes how well matched a patient and donor are. The major histocompatibility determinants are the human leukocyte antigens (HLA). HLA typing is performed between a potential marrow donor and the potential transplant recipient to determine how close a HLA match the two are. The closer the match the less the donated marrow and the patient's body will react against one another.