Five children with severe sickle cell anaemia underwent an HLA compatible allogeneic bone marrow transplantation. In four children the engraftment was rapid and sustained. The fifth child rejected the bone marrow graft and required a second bone marrow transplantation 62 days after the first one. The outcome was then uneventful. In all cases there was complete cessation of vaso-occlusive episodes and haemolysis. The haemoglobin electrophoretic pattern became similar to that of the donor (AA or AS) and cytogenetic studies in three patients confirmed the donor origin of bone marrow cells.