elevation of cablmrna in human leukemic b lymphoblasts analysis of vablhomologous transcripts in peripheral blood leukocytes from 20 leukemia patients revealed a 5kb species as the major ablmrna present elevated levels of this 5kb transcript together with detectable levels of 2 and 10kb ablhomologous species were observed in mrna samples from two patients one with philadelphia chromosome phpositive chronic myeloid leukemia cml in lymphoid blast crisis and the other with childhood burkitttype blymphoblastic leukemia these ablhomologous transcripts differed from the aberrant 8kb ablmrna reported by others in phpositive cml patients in both size and extent of vablhomology no alteration in the organization of vablhomologous sequences was detected in the genomic dna of the phpositive cml patient karyotypic analysis of the burkitttype blymphoblastic leukemia patient revealed the presence of an 814 translocation together with a number of other chromosomal aberrations however no abnormality of chromosome 9 could be detected hence the observed increase in cabl transcription is not consistently associated with either gross gene rearrangement or presence of the ph the high levels of cabl mrna may be a function of the cell type involved early lymphoid blast suggesting that failure to downregulate cabl may be a factor in the onset of pre or early blymphoid leukemias