A novel human myeloid leukaemia cell line (HNT-34) was established from the peripheral blood of a 45-year-old female patient with acute myelogenous leukaemia (AML) transformed from chronic myelomonocytic leukaemia (CMMoL) with 3q21q26 syndrome. Morphologically, the HNT-34 cells were undifferentiated blasts which were negative for myeloperoxidase. The HNT-34 cells were positive for CD4, CD13, CD33 and CD34, but negative for CD41a and CD42b. The cells actively proliferated in suspension with a doubling time of 26-27h in the absence of any growth factors. Neither proliferative advantage nor differentiation was observed with the addition of G-CSE GM-CSF, IL-3, TPO, DMSO or PMA. Cytogenetic analysis showed 46,XX. t(3;3)(q21;q26), t(9;22)(q34;q11),20q-. Molecular analysis showed expression of EVI1 gene, P210 and P190 BCR/ABL chimaeric transcripts. The chromosomal breakpoint at 3q26 of HNT-34 cell line was located to approximately 200 kb 5' of FIM3 locus and more upstream of the MDS1. which is the same region as that of somatic cell hybrid line H10C. The breakpoint at 3q21 was located within the 390 kb centromeric from the breakpoint cluster region. These results suggest that the HNT-34 cell line may be a useful tool for the elucidation of the mechanisms of leukaemogenesis which involve the 3q21q26 syndrome and Ph1 chromosome.