One hundred thirty‐one children between 1 and 15 years of age have been treated. Ninety‐five children had acute lymphoblastic leukemia (ALL); 13 had other types of leukemia; 8 had lymphoma; and 15 had other solid tumors. The dosage ranged from 10 to 5,000 IU/kg daily. Treatment schedules included maintenance after remission and no maintenance. Nine patients in bone marrow remission with other chemotherapy prior to treatment with A‐ase received a 28‐day course. Six patients received the enzyme intrathecally for meningeal leukemia. Of the 73 adequately treated (over 14 days) ALL patients, the overall remission rate was 62%; the median duration of remission was 60 days with a range of 15 to 248 days. The duration of remission appeared to be independent of dose. Six nonlymphoblastic leukemias demonstrated transient fall in WBC and decreased organ size but no bone marrow remission. One of 4 with Hodgkin's disease demonstrated decrease in size of nodes, liver, and spleen. None of the solid tumors responded. The usual side effects of conventional chemotherapeutic agents, mucous membrane ulcerations, alopecia, and diarrhea were not seen. Side effects included reversible abnormal biochemical liver function tests, fever, and anaphylaxis.