A 10-year-old girl suffering from post-hepatitic aplastic anaemia received 21 x 10(10) (5 x 10(8)/kg body weight) nucleated cells from her brother, whose HLA typing, but not his blood group, was identical with the patient's. Conditioning had been carried out with cyclophosphamide according to the Seattle protocol (50 mg/kg body weight on four successive days). On day 9 she showed signs of early engraftment by the appearance of granulocytes and their precursor cells in the peripheral blood. The new blood group of the patient's erythrocytes and the male karyotype of her leucocytes demonstrate successful engraftment. The child is now in excellent health 18 months after transplantation and requires no treatment of any kind. This paper reports the first bone-marrow transplantation in Austria.