Genetic diseases can be treated by transplantation of normal allogeneic bone marrow. Four patients with congenital disorders of their hematopoietic and/or lymphoid stem cells have been transplanted. One patient had a congenital aplastic anemia (Blackfan-Diamond), one had Gaucher's disease, one had congenital agranulocytosis Kostmann and one had chronic granulomatous disease. All patients received busulfan, cyclophosphamide and total nodal irradiation as preparatory regimen. Total nodal irradiation and cyclophosphamide were used as immunosuppressive agents. In all cases hematopoietic ablation and donor lymphoid and hematopoietic engraftment were achieved. The basic disorders of all transplanted children could be corrected completely. All children are alive and well.