Research investigations of general practice on the prevention of cardiovascular disease indicate that preventive detection and intervention programmes can be effective. Long-term results on hypertension control are better when systematic follow-up accompanies surveillance of the hypertensive population. Based on research and international experience, we developed the Nijmegen Hypertension Monitoring System, a computer-assisted system consisting of monthly feedback of treatment results and regular meetings of the participating general practitioners. We describe an experiment in seven study practices and eight practices continuing with usual care, to study the effectiveness and feasibility of the system. This Monitoring System could also be adapted for other chronic diseases.