1. One major subprogramme of the North Karelia Project was the hypertension programme which aimed at lowering of the high blood pressure among the whole population, and especially among middle-aged men. The hypertension programme consisted of intervention integrated with the existing health care structure of the county of North Karelia.
2. The hypertension register, which was the major tool of the programme, aimed to maintain patients in treatment and to get information about the development of the programme. Registration of hypertensive subjects was continuous between 1972 and 1977 and registered patients had annual follow-up examinations.
3. After 5 years of the programme, there were approximately 17 000 registered patients which is 9·7% of the total population.
4. Proportion of drop-outs at the annual follow-up examinations was less than 10%. 83% of the registered hypertensive subjects were under drug treatment after 3 years intervention. The percentage of normotensive subjects increased significantly year by year.
5. Preliminary results from the stroke register of the North Karelia Project indicate that the incidence of stroke decreased as hypertension control was improved.