Oral anticoagulation therapy with coumarins (e.g. warfarin (Marevan®) has a narrow therapeutic index, and monitoring is based on the International Normalized Ratio (INR). The management can be optimised using patient self-management, which implies that the patient analyses a drop of blood using a portable coagulometer. The coagulometer displays the INR, according to which the patient finds the dosage of coumarins. Research in this area implies both clinical aspects and investigation of coagulometers.