In most centers allogeneic bone marrow transplantation is restricted to patients with HLA-identical siblings as donors. We have transplanted 16 patients with marrow of donors other than HLA-identical siblings. Seven patients were grafted in the years 1978 until 1984. Six died of transplant complications and one of recurrent leukemia. More recently 9 patients were transplanted following an improved immunosuppressive conditioning treatment derived from experimental studies in dogs. Four are alive and in continuous remission between more than 2 months and 2 years. 5 patients died, 3 from fungal infections, one from recurrent leukaemia and one early from endothelial leakage syndrome. Our results indicate that intensified immunosuppressive conditioning may improve the results of marrow transplantation from HLA-haploidentical donors.