The results of therapy with cytosine arabinoside as a single chemotherapeutic agent in 31 consecutive patients with acute granulocytic leukemia receiving 40 courses of therapy are reported. The initial complete remission rate in the evaluable course of therapy was 46 per cent. The morphological classification of the leukemia, age of the patient, and rate of deoxyribonucleic acid (DNA) synthesis by the leukemic leukocytes in tissue culture were correlated with the rate of complete remission. Maintenance therapy with 6-thioguanine did not significantly increase the length of initial remission in this series.