Six hundred and eighteen patients with acquired aplastic anaemia grafted from an HLA-identical sibling donor between 1976 and 1990 in eight European centres were reported to the Working Party for Severe Aplastic Anaemia (SAA) Registry and were evaluable for analysis of the incidence of graft failure/rejection and the outcome of second bone marrow transplants (BMT). The number of patients experiencing graft rejection declined significantly over the study period from 32% to 8% (p < 0.0001). This coincided with the introduction of cyclosporine to the conditioning regimen for BMT. The graft rejection rate in the post-hepatitis SAA group was significantly lower than in the group with idiopathic SAA (4% vs 20%) (p = 0.001). The use of irradiation in the conditioning regimen significantly reduced the number of patients experiencing graft rejection (7% vs 21%) (p = 0.004). Age, sex and severity of disease did not influence the rate of sustained engraftment. Of the 85 patients experiencing graft rejection, 41 received a second transplant: their survival is 33% vs 8% for patients not transplanted a second time (p = 0.003). The major factor predicting the outcome of second BMT for SAA was the interval from first BMT. Patients receiving a second BMT within 60 days from the first BMT had a significantly poorer outcome.