- To evaluate the adequacy of oral anticoagulation therapy in patients with either prosthetic heart valves or atrial fibrillation. Adequacy of anticoagulation therapy of patients treated with warfarin was determined before and after implementation of an improvement programme. The central haematology laboratory of the Soroka Medical Center, Beer-Sheba Israel. One hundred and ten patients treated with chronic anticoagulation therapy were evaluated by measuring the international normalized ratio of the prothrombin time before and after implementation of an improvement plan aimed at improving anticoagulation control. A programme that included physician and patient education and procedural changes covering all aspects of anticoagulation therapy was implemented. The percent of international normalized ratio tests below, within and above the therapeutic range was determined. Prior to implementation of an improvement plan, only 32% of the measured international normalized ratio values were within the therapeutic range. 16% were above and 52% were below therapeutic range. Improvement intervention led to an increase in the proportion of international normalized ratio tests that fell within the therapeutic range from 32% to 43.2%. Improvement in the control of anticoagulation therapy of patients receiving long-term warfarin treatment is possible. A combined effort involving the community, physician and patient is required.