Attempts to improve the efficacy of pretransplant conditioning regimens have been published, the potential of a better antileukemic effect being impaired by more frequent and severe toxicities. The efficacy of an intensified regimen, TAM (TBI, high-dose cytosine arabinoside and melphalan), is evaluated by analyzing long-term follow-up of a homogenous group of 42 high-risk ALL patients allografted in first CR. Age at time of BMT was 25.9 +/- 10.4 years (3-41). Twenty-two patients had more than three adverse prognostic factors. Ten patients had a Ph chromosome. Probability of overall survival was 45 +/- 9%, and for all surviving patients median follow-up time was 66 months. Event-free survival was 40 +/- 8% at 7 years after transplantation and the expected relapse rate reached 31%. Twenty-two deaths occurred, six after a relapse but 16 appeared to be directly due to the BMT procedure. None of the pretransplant characteristics significantly affected outcome after BMT. TAM appeared to be an efficient antileukemic therapy for conditioning high-risk ALL patients before allogeneic transplantation, but was still very toxic. The use of TAM in adult ALL patients in first CR is not recommended and the real role of intensified conditioning regimens remains to be demonstrated.