Thirty patients with advanced acute leukemia and lymphoma were treated with the sequential combination of high dose ARA-C (HiDAC 3 gm/m2 infused i.v. over 3 h at 0, 12, 24, 36 h) and asparaginase (ASP 6.000 IU/m2 i.m. at hour 42). The sequence was given on day 1 and 8 irrespective of the degree of myelosuppression. Of 22 patients with leukemia there was only one who was absolutely refractory to therapy. Complete remission was induced in 3 patients with ANLL (30%) and in 3 with ALL (30%). Three patients became hypoplastic but recovered with blasts and 12 died from infection, complicated by intracranial hemorrhage in 3, during hypoplasia. Of 8 patients with lymphoma, 2 were clearly refractory to therapy, one died from sepsis and the remaining 5 all entered remission (2 CR + 3 PR, 62%). Activity of HiDAC/ASP against CNS disease is suggested by the clinical response seen in patients with overt meningeal or intracerebral involvement. Toxicity associated with HiDAC/ASP was mainly hematologic. All but one patient experienced hypoplasia and severe pancytopenia; documented infections and major hemorrhages occurred in 80 and 20% of patients respectively. We conclude that HiDAC/ASP is a regimen with definite activity against acute leukemia and lymphoma including CNS disease. Alternate treatment schedules should be explored in order to reduce marrow toxicity.