Sixty-three unselected Japanese cases of acute leukemia studied with chromosomal banding techniques and their hematologic and clinical evaluations were made. Salient features of this study were as follows: (1) Cases with t(8;21),t(15;17), and t(9;22) had characteristic clinical features, respectively; in particular, those with t(8;21) showed different hematologic findings than patients with other karyotypes with M2 type of leukemia. (2) Among cases of M0, M1, and M2 with normal karyotypes, those with initial white blood cell counts less than 2.0 × 10 4/ mm 3 responded well to initial chemotherapy and had long remission durations, whereas most cases with white blood cell counts of more than 10.0 × 10 4/ mm 3 failed to undergo first remissions and had a poor prognosis, (3) Acute nonlymphocytic leukemia patients with abnormal karyotypes, including t(8;21) and t(15;17), relapsed within 10 mo after the first complete remission, and no remarkable correlation between the specific chromosome changes and remission duration was observed.