A meeting took place in Helsinki in November 1989 to consider the scientific, clinical and financial implications of establishing a registry of volunteer bone marrow transplant donors in the Nordic countries. The possible contributions of new techniques for defining HLA genes and gene products, notably the study of restriction fragment length polymorphisms and allele specific oligonucleotides, and for selecting optimal donors, notably the assay of cytotoxic T lymphocyte precursors in the graft-versus-host direction, were discussed. The differing approaches actually used to establish new donor registries in the United Kingdom, United States and France were contrasted. The clinical results of using unrelated donors for transplanting patients with chronic myeloid leukaemia, severe aplastic anaemia and other haematological diseases were presented. Finally, participants heard details of the International Marrow Unrelated Search and Transplant Study which collects and analyses data internationally on patients for whom searches are initiated and on patients who actually receive transplants from volunteer donors.