Early bone marrow transplantation (BMT) in leukaemia has enormously improved the results. Leukaemic relapse is rare, as is transplant-related mortality from interstitial pneumonia and severe graft-versus-host disease (GvHD). In aplastic anaemia the most important development is that treatment with ALG offers a real alternative to BMT which is of crucial importance for all patients without a histo-compatible family donor. The main problems of BMT are the lack of histocompatible donors and GvHD. In leukaemia, relapse is still an additional problem. The new immunosuppressive agent cyclosporin-A (CyA) has made an important contribution to the prophylaxis of severe GvHD. In future the results with CyA are potentially improvable by combination with other immunosuppressive agents. It is important that the use of HLA-semicompatible family donors, unrelated donors or alternative stem cell sources should become feasible. The value of autologous BMT is difficult to judge because in most instances it has been performed in patients with endstage disease. In several congenital diseases there are alternatives to BMT, such as genetic engineering. Although many problems of BMT still have to be solved, this procedure has an important place in modern medicine.