The Philadelphia (Ph) chromosome can be detected in chronic myelogenous leukemia (CML) and a significant number of acute lymphoblastic leukemia (ALL) cases. Generation of p210bcr/abl, a chimeric protein with enhanced kinase activity, is thought to be involved in the pathogenesis of these diseases. To elucidate the biological properties of p210bcr/abl and to create an animal model for human Ph1-positive leukemias, we generated transgenic mice expressing p210bcr/abl driven by the promoter of the tec gene, a cytoplasmic tyrosine-kinase preferentially expressed in the hematopoietic lineage. The founder mice showed excessive proliferation of lymphoblasts shortly after birth and were diagnosed as suffering from ALL based on surface marker and Southern blot analyses. Expression and enhanced kinase activity of the p210bcr/abl transgene product were detected in the leukemic tissues. In contrast, transgenic progeny exhibited marked granulocyte hyperplasia with thrombocytosis after a long latent period and developed myeloproliferative disorders (MPDs) closely resembling human CML. Expression of p210(bcr/abl) mRNA in the proliferating granulocytes was detected by RT-PCR. In particular, one MPD mouse showed remarkable proliferation of blast cells in the lung, which might represent an extramedullar blast crisis. The results demonstrate that the expression of p210bcr/abl in hematopoietic progenitor cells in transgenic mice can contribute to two clinically distinct hematopoietic malignancies, CML and ALL, indicating that this transgenic system provides a novel transgenic model for human Ph1-positive leukemias.