Fourteen patients with hematologic neoplasia (11 acute myeloid leukemias, 2 non-Hodgkin’s lymphomas and 1 blast crisis of chronic myeloid leukemia) who underwent high-dose cytosine arabinoside (HIDARAC) therapy with or without sequential asparaginase (ASNase) were investigated in order to evaluate liver toxicity and a possible decrease in antithrombin III (AT III) plasma level. AT III was found decreased only in patients who received ASNase, whereas HIDARAC alone did not influence AT III levels. It is pointed out that a single dose of ASNase seems to be sufficient to induce a decrease in AT III. A mild and transient liver toxicity due to HIDARAC therapy does not seem to be of any clinical relevance.