The prolongation of the APTT and PT by heparin can be neutralized by treating the plasma with heparinase or with certain anion-exchangers. The purpose of the present study was to assess the effectiveness of a new commercial heparinase reagent. Heparinase (Hepzyme) for the removal of heparin from plasma was compared with ECTEOLA-cellulose treatment. In ex vivo heparin samples, shorter APTT values were obtained with heparinase than with ECTEOLA-cellulose, suggesting that the former treatment is more effective for the removal of heparin from plasma. Heparinase (Hepzyme) treatment may be used to improve INR assessment in patients treated with heparin and oral anticoagulants concomitantly.