To optimise a one step reverse transcriptase polymerase chain reaction (RT-PCR) protocol for BCR-ABL chimaera detection. Compared with published RT-PCR procedures, this novel approach has at least two advantages. First, the same enzyme is used for both reverse transcription and PCR. Second, amplification of the target (BCR-ABL chimaera) and control gene (ABL) is performed simultaneously in the same tube. On testing 40 chronic myelogenous leukaemia patients and 10 healthy donors there was a specificity for the newly developed technique. In addition, dilution experiments demonstrated that the protocol was highly sensitive. The suggested one step PCR strategy is a simple and reliable way to reveal BCR-ABL chimaeras.