Résumé : Background: L-asparaginase, a key therapeutic agent in the management of patients with acute lymphoblastic leukemia (ALL), dramatically impairs hepatic protein synthesis. We investigated the effects of prolonged exposure to L-asparaginase on antithrombin (AT), fibrinogen and mannan-binding-lectin (MBL) levels, and on the occurrence of thrombotic events (TE) and febrile neutropenia episodes (FN) in pediatric patients. Procedure: Protein levels were measured in 97 children during 30 weeks of chemotherapy with L-asparaginase and up to 1 year following remission. TE and FN episodes were recorded during this period. Results: Median AT level decreased from 0.96IU/mL prior to treatment (range: 0.69-1.38) to 0.55IU/mL (0.37-0.76) during therapy. Fibrinogen and MBL decreased from 3.18g/L (1.29-7.28) and 1,177ng/mL (57-5,343) to 1.56g/L (0.84-2.13) and 193ng/mL (57-544), respectively. All three proteins had recovered 1-4 weeks after L-asparaginase cessation. TE were reported in 22 (23%) patients. Of these, 11 occurred after a median of 10 administrations of L-asparaginase. Fifty-one FN were associated with infections, of which 36 occurred during treatment with L-asparaginase. Patients with low levels of MBL at diagnosis were at higher risk of FN associated with infections (RR=1.59, 95%CI: 1.026-2.474). Both AT and MBL decreases were moderately correlated with fibrinogen (r=0.51 and 0.58, respectively). Conclusions: Children with ALL are exposed to significant decrease in AT, fibrinogen and MBL levels, and concomitant increased risk of thrombosis and FN with infection during L-asparaginase treatment. Measuring plasma levels of these liver-derived proteins could help predict the occurrence of adverse events.