In an attempt to improve the chemotherapy of acute leukemia in adults, the author has studied the induction therapy on 63 cases with acute leukemia with Neocarzinostatin (NCS; N) in combination with conventional antileukemic agents; Vincristine (V), Daunorubicin (D), Cytosine Arabinoside (A), 6-Mercaptopurine-Riboside (M) and Prednisolone (P). Eighteen cases with acute lymphocytic leukemia (ALL) was treated with protocol A (NVMP, NDMP, NAMP). Out of 45 cases with acute non-lymphocytic leukemia (ANLL), 25 was treated with protocol A and 20 treated with protocol B (NADP, NAVP), and obtained the following results. 1) Of all 63 cases 51 (81.6%) attained complete remission and 9 (14.3%) partial remission. 2) Complete remission was obtained in 15 cases (83.3%) out of 18 with ALL and 36 cases (80.0%) of 45 with ANLL; the latter cases with ANLL consisted of 18 of 25 cases (72.0%) treated with protocol A and 18 of 20 cases (90.0%) with protocol B. 3) Refractory varieties included cases with acute myelogenous leukemia who had passed through atypical hematological findings, cases with monocytic leukemia, cases with WBC count over 50,000 per μl or with nucleated cell count in bone marrow over 500,000 per μl before treatment and cases over 50 years old. 4) In this induction therapy with NCS in combination, antileukemic effects was remarkable, while suppression on normal hematopoiesis, especially on thrombocytes, was very slight. 5) As to the other side effects no noteworthy disturbances other than occasional nausea, anorexia and liver damage in protocol B were observed. From these results it can be concluded that NCS in combination is one of the most potent remission induction therapies in acute leukemia in adults.