A 26 year old Japanese male who had a history of leukocytosis in 1985 and received chemotherapy because of myeloblastic crisis of chronic myelogenous leukemia (CML) from May 1986, was admitted in November 1987. He had lymphadenopathy, lymphoid tumor of paranasal sinus and pleural effusion with marked lymphoid cells infiltration. On admission, laboratory data of peripheral blood and bone marrow revealed remission; lymphoid cells of pleural effusion were positive for CD3, CD4 and CD8. Second induction chemotherapy was performed successfully. After a few months, however, myeloblastic crisis recurred. Intensive chemotherapy ended in failure and he died of renal and heart failure. Chromosome analysis showed Ph1 and additional abnormalities at myeloblastic crisis and normal at T lymphoid crisis, but the same rearrangement of breakpoint cluster region existed in both crisis cells. Therefore we supposed that more than two-step pathogenesis is involved in the development of Ph1 positive or Ph1 negative CML clone of this patient.