The purpose of this study is

1. to determine the correct dose for intramuscular administration
2. to compare the frequency of antibody formation after intramuscular administration of native E.coli asparaginase and PEG-asparaginase during two treatment courses in the treatment of childhood lymphoblastic leukemia

Asparaginase is used in the treatment of childhood lymphoblastic leukemia. Approximately 1/3 of the patients develops blocking antibodies against native E.coli asparaginase during the second exposure, so that they do not benefit from treatment and thus may have a worse prognosis.

PEG-asparaginase is less immunogenic so that fewer patients may develop antibodies during the second exposure.

There is no published study about the antibody formation after treatment of children with PEG-asparaginase during two treatment courses.

The first part of the study is a description of the pharmacokinetics of PEG-asparaginase after intramuscular administration in order to determine the correct dose.

The second part of the study is a comparison of antibody formation during two treatment courses after intramuscular administration og native E.coli asparaginase and PEG-asparaginase.

Other side effects than antibodies will be registered during treatment with PEG-asparaginase. Finally comparison of the 5-year EFS between the groups (native E.coli asparaginase and PEG-asparaginase as well as patients who have and have not developed antibodies) will be evaluated.

Inclusion Criteria:

• 1-17 years
• Newly diagnosed ALL (high intensive)
• Treated according to the NOPHO-2000 protocol
• Treated at one of the Nordic pediatric oncology centers

Exclusion Criteria:

• <1 year and >18 years
• Newly diagnosed ALL other than high intensive
• Not treated according to the NOPHO-2000 protocol
• Not treated at one of the Nordic pediatric oncology centers
• Allergy to the contents
• Pancreatitis (Active or earlier)