Longitudinal RT-PCR monitoring of the PML/RARα fusion gene in BM samples collected before and after ABMT. Following RT-PCR characterization of relapse, all pretransplantation (pre-ABMT) and posttransplantation (post-ABMT) tests were performed while patients were in hematologic remission. Black and white circles indicate positive and negative RT-PCR tests, respectively. 1st REL, first relapse; R, hematologic relapse; ↓ sec. leukemia, this patient developed at 36 months a secondary (or therapy-related) leukemia whose blasts tested RT-PCR⁻ for the PML/RARα hybrid. Numbers above the white (open) circles indicate the last follow-up control, in months, after achievement of second remission.