We have developed a titration assay using a competitive reverse transcriptase polymerase chain reaction (RT-PCR) which is able to estimate the number of AML1/ETO transcripts so that minimal residual disease (MRD) can be monitored quantitatively in patients with t(8;21) acute myelogenous leukaemia (AML).     ///    "Using a qualitative RT-PCR method, AML1/ETO transcripts could be detected in all samples from 15 first PBSC harvests and 11 second PBSC harvests obtained from 15 patients with t(8;21) AML. "    ///    Quantitative analysis of AML1/ETO transcripts in peripheral blood stem cell harvests from patients with t(8;21) acute myelogenous leukaemia..     ///    "With our competitive RT-PCR assay, the number of AML1/ETO transcripts was found to be lower in the second PBSC harvest than that in the first in every individual. "    ///    "In 10 patients who received autologous blood stem cell transplantation (ABSCT), we could not find a relationship between the number of AML1/ETO transcripts in the infused PBSC harvests and the clinical outcome after ABSCT. "