G-banded cytogenetic studies of 3 male patients in the terminal phase of chronic myeloid leukemia showed the following abnormalities: in the first case, the presence of a medullar cell line with 51 chromosomes and 3 Ph1; in the second case, a clone with 65 chromosomes and 4 Ph1, and in the third patient a clone with 53 chromosomes and 3 Ph1. In all 3 cases, G-banding revealed the Ph1 translocation to be of the usual type: t(9;22) (q34;q11) and there was discordance between the number of Ph1 and 9q+. There was no obvious correlation between the presence of multiple Ph1 and the clinical or cytological features. These 3 cases were detected as part of a recent G-banded cytogenetic survey of 9 individuals in the blastic phase studied by the authors. The frequency of multiple Ph1 observed in this sample of blastic-phase leukemia is unusually elevated, raising the question of the origin of such a high incidence.