Expression of the cellular abl (c- abl ) oncogene was studied in K-562 and other chronic myelogenous leukemia (CML) cells and cell lines by means of Northern blot hybridization. In contrast to non-CML cells, which contained 7.4- and 6.8-kilobase abl -related transcripts, the CML cells contained a predominant and novel 8.2-kilobase abl -related RNA. In addition, the levels of abl -related message were up to eight times higher in CML cell lines from patients at the blast crisis stage of the disease compared with CML cells obtained during the chronic phase and with non-CML cells.