We have developed a competitor-based RT-PCR techniqueation with the FAB subtype M4Eo, and some groups using an which will detect and quantitate the CBF␤/MYH11 transcripts RT-PCR have found it exclusively in M4Eo, 4 while others have associated with inv(16)(q22;p13) and have used it to study found the abnormality in cases of M4 lacking abnormal presentation and follow-up samples of acute myeloid leueosinophils. 6 The sensitivity of the PCR test has allowed it to kaemia (AML). The levels of the leukaemia-specific transcripts be used to monitor residual disease following treatment, 4,6,7 are expressed as a ratio to a ubiquitously expressed mRNA species (Abl) which controls for RNA degradation. This techand PCR positivity has been found in patients in long-term nique has been applied to 75 consecutive patients presenting remission. 6,7 with either de novo AML or tMDS; 6/75 patients analysed wereIn a study of four patients with inversion (16) in patients in complete remission.