We studied the kinetics of EBV-transformed B-cell lines from patients with chronic myeloid leukaemia (CML) using RT-PCR for BCR-ABL transcripts and immunoglobulin heavy chain (IgH) gene rearrangements. Peripheral blood mononuclear cells, obtained from four patients with CML in chronic phase and from one in accelerated phase, were incubated with supernatant from the B95-8 EBV producing cell line. In 11/25 (44%) B-cell cultures established we demonstrated the presence of BCR-ABL transcripts at intervals ranging from 32 to 125 d post EBV transformation. In all but two cases, evidence of BCR-ABL transcripts disappeared with time. Cultures were initially polyclonal with respect to IgH rearrangements but became progressively oligoclonal, suggesting the longer-term survival of fewer clones, all of which were BCR-ABL negative. We conclude that BCR-ABL-positive lymphoid cultures can be established in the short term from the majority of patients with CML but they have limited capacity to survive in the longer term. Therefore, in lymphoid cells the presence of the BCR-ABL chimaeric gene appears to confer no survival advantage.