Although L-asparaginase (ASP) is associated with several toxicities, its myelosuppressive effect has not been well characterized. On DFCI ALL Consortium Protocol 05-01 for children with newly diagnosed acute lymphoblastic leukemia, the Consolidation phase and the initial portion of the Continuation phase were identical for standard risk patients, except ASP was given only during Consolidation. Comparing the two treatment phases revealed that low blood counts during Consolidation with ASP resulted in more dosage reductions of 6-mercaptopurine and methotrexate. The myelosuppressive effect of ASP should be considered when designing treatment regimens to avoid excessive toxicity and dose reductions of other critical chemotherapy agents.