At the Third Conference on Histocompatibility Testing, held at Saint-Vincent, Italy, in July 1967, the participants agreed to appoint, by postal vote, a Nomenclature Committee drawn from among specialists in tissue typing, immunology and human genetics; that Committee was asked to propose a nomenclature for leucocyte antigens, which, it was hoped, might prove internationally acceptable. The Secretariat of the World Health Organization was asked to facilitate and assist in the work of the Committee. The following is the text of the memorandum drawn up by the Committee.(1)