 RATIONALE: L-asparaginase is an important component of treatment for childhood acute lymphoblastic leukemia, but is also associated with notable side-effects, including hypersensitivity, pancreatitis, and thrombosis. We have previously reported that patients with acute lymphoblastic leukemia in whom asparaginase treatment was discontinued because of intolerable side-effects had survival outcomes that were inferior to those who received all or nearly all of their intended doses. Two bacterial sources of asparaginase exist: Escherichia coli E coli and Erwinia chrysanthemia Erwinia. Generally, the E coli-derived enzyme has been used as front-line therapy and the Erwinia-derived preparation has been reserved for patients who develop hypersensitivity reactions. Pegylated E coli asparaginase PEG-asparaginase has a longer half-life and is potentially less immunogenic than native E coli L-asparaginase, and has been used as the initial asparaginase preparation in some pediatric acute lymphoblastic leukemia treatment regimens. 