It is unclear how best to treat children with acute lymphoblastic leukaemia (ALL) who are in a second remission. Treatment with bone-marrow transplants from HLA-identical siblings results in a statistically greater likelihood of leukaemia-free survival than does chemotherapy. Less than 25% of relapsed patients are able to benefit from this therapy due to a lack of matching donors; chemoradiotherapy or autologous BMT are considered for the rest. We compared treatment results for children who underwent autologous BMT with those who had chemotherapy. All patients were registered between 1983-94 in the multicentre trials. We selected groups of patients by matching variables associated with treatment outcome and duration of second remission. 52 matched-pairs were studied. The probability of event-free survival at 9 years was 0.32 (SD 0.07) for patients receiving chemotherapy versus 0.26 (SD 0.07) for patients who underwent autologous BMT. For two groups--children with prognostic factors indicating high risk of relapse and those with factors indicating lower risk--the outcome from transplantation did not differ significantly from that of chemotherapy: no advantage of autologous BMT over chemotherapy as post-induction treatment for children with ALL in a second remission could be detected with regard to event-free survival. Because autologous BMT has been used as the final step of treatment it is possible that its relative ineffectiveness has been due to the lack of continuation therapy after transplant. Attempts should be made to complement autologous BMT by subsequent immunotherapy, molecular biotherapy, chemotherapy, or a combination of these.