Human DNA ligase was purified from both normal and leukemic peripheral lymphocytes and normal thymocytes. The activity of the purified enzymes was assayed in the presence of several widely used antileukemic drugs. Melphalan and prednisone at 5 nriMhad no effect. Carmustine, chlorambucil, and cyclophosphamide were more effective at inhibiting the enzyme from leukemic cells, whereas Adriamycin an...