Abstract Hybrid cell lines were derived from fusion of rodent cells with leukocytes from a t(9q+ 22q−)-positive chronic myeloid leukemia (CML) patient carrying a chromosome No. 9-linked adenylate kinase-1 (AK1) polymorphism (AK1 1–2). The AK1∗2 allele was consistently expressed when 9q+ was present, whereas the AK1∗1-coded isozyme was formed when the normal chromosome No. 9 was present. These results provide additional data confirming the clonal origin of the Ph 1 translocation in CML.