Although the majority of bone marrow transplants (BMT) have been performed using HLA-identical sibling donors, BMT may also be successful when the donor is a haploidentical partially matched relation or a well-matched unrelated volunteer. For patients with acute lymphoblastic leukaemia or acute myeloid leukaemia, an alternative to allogeneic BMT using a sibling donor is the use of autologous marrow, although the period of follow-up for such studies is still relatively short and final assessment must await the results of randomized trials. In contrast patients with chronic myeloid leukaemia, severe aplastic leukaemia or myelodysplasia who lack suitable related donors are prime candidates for well-matched unrelated donor transplantation. In this paper we discuss the value of various methods for identifying unrelated donors, the size and costs of maintaining volunteer panels in relation to the probability of finding a matched donor for an individual patient and some of the criteria on which the choice between a mismatched family member donor and a matched unrelated donor can be based.