Severe coagulopathies can occur during liver transplantation, particularly after reperfusion of the grafted liver. Heparin release has been proposed as one of the factors contributing to this coagulopathy. We have analysed the thrombelastograph (TEG) traces of 55 patients after reperfusion using native and heparinase-treated samples. In almost all cases an abnormal native TEG was improved in vitro by heparinase, demonstrating the presence of heparin or a heparin-like substance. The heparinase-modified TEG allowed assessment of the underlying coagulation status, providing a rational guide to blood component replacement or treatment of fibrinolysis.