Chronic myeloid leukemia (CML) was diagnosed in a 19-year-old man in 1961, and the disease remained in chronic phase, with occasional exacerbations, for 27 years. In 1976, when the first cytogenetic analysis was performed, t(9;22)(q34;q11) was found as the sole abnormality in all mitoses. During accelerated phase in 1988, a second cytogenetic investigation showed the karyotype 45,XY,t(9;22)(q34;q11),-15,-17,+der(15) t(15;17)(p13;q11). Molecular analysis revealed a rearrangement in the 5' end of the major breakpoint cluster region (M-bcr). With the case presented here, sublocalization of the bcr breakpoint has now been undertaken in altogether five CML patients with extremely long survival. It is noteworthy that in all these cases the chromosome 22 breakpoint was located in the 5' region of the M-bcr.