Retrospective comparison of qualitative and quantitative reverse transcriptase polymerase chain reaction in diagnosing and monitoring the ALL1-AF4 fusion transcript in patients with acute lymphoblastic leukaemia..     ///     We compared quantitative reverse transcriptase polymerase chain reaction (Q-RT-PCR) to qualitative RT-PCR in determining response to therapy and predicting clinical outcome in 18 retrospectively selected patients with ALL positive for the ALL1-AF4 fusion and with frozen RNA samples collected at diagnosis and during follow-up (96 samples analysed).     ///    "The ALL1-AF4 junction was detected by qualitative RT-PCR in 18 patients and by Q-RT-PCR in 17 patients (one patient harboured the rare e10-e6 ALL1-AF4 junction, which falls outside of the primer and probe location designed for the Q-RT-PCR). "    ///    "In three of the 12 patients negative to qualitative RT-PCR after induction therapy, a small number of ALL1-AF4 copies was detected by Q-RT-PCR. "