Three out of 21 patients treated at the Children's Hospital of Eastern Switzerland for ALL or NHL with the respective BFM-90 protocols experienced thrombotic complications during Erwinia L-asparaginase therapy. We therefore investigated the development of the haemostatic imbalance in six children during the induction phase of both protocols. In the average, elevated thrombin generation was found simultaneously to an increase in fibrinogen, cross-linked fibrin degradation products and platelet counts between protocol days 28 to 35. This period thus seems to harbour an increased potential of hypercoagulability which could explain the accumulation of thrombotic complications described by Sutor et al. Moreover, day to day investigations just before and one day after L-asparaginase administration did not show any relevant change in the above named parameters, thus rather indicating a cumulative than a single dose effect of Erwinia L-asparaginase therapy on the coagulation system. These findings lead to the question if the prophylactic use of anticoagulants might reduce the hypercoagulability seen during L-asparaginase therapy, which is currently under investigation in our institutions.