Background: Asparaginase (Asp) and corticosteroid (CS) treatment in patients with acute lymphoblastic leukaemia (ALL) is associated with an increased risk of thrombotic events. Objective: Characterization of global haemostatic phenotypes of patients with ALL during Asp therapy. Procedure: Thrombin generation (TG) was monitored in platelet-poor plasma of 56 children treated for a B lineage ALL (36 with native, 20 with PEG Asp) using 1 pM tissue factor and 4 μM phospholipids, with and without thrombomodulin. Protein C activity (PC), free protein S (PS), antithrombin (AT) and fibrinogen levels were also measured. Results: Elevated endogenous thrombin potential (ETP) and peak of TG were noted at diagnosis, throughout the Induction phase and Late Intensification but was significantly less for PEG than for native Asp (P