Three areas of bone-marrow transplantation have developed particularly rapidly during the past year. First, increasing numbers of bone-marrow transplants using matched unrelated donors or HLA-mismatched family members have been successfully performed. Second, trials of recombinant hemopoietic growth factors have shown these agents can accelerate hemopoietic recovery after bone-marrow transplant and reduce the incidence of infections and other post-transplant complications. But potentially the most important advances have come in a series of separate observations, which in conjunction suggest mechanisms by which the anti-leukemic activity of an allograft may be separated from its ability to induce graft-versus-host disease.