The population aged 40 to 64 years of the municipality of Köyliö, situated in southwestern Finland, was screened for hypertension in 1973-74; a total of 1018 persons (92%) participated in the program. On the basis of two separate blood pressure measurements a total of 147 hypertensive individuals who were not under treatment were identified. These individuals were divided into two groups by randomization of matched pairs. One group (the control group) was merely advised by letter to see a physician for raised blood pressure, while the other group (the experimental group), in addition to being so notified, received written information explaining the nature of hypertension and the importance of its treatment. After two years, the individuals in both groups were invited for a follow-up blood-pressure measurement, with the object of investigating the number of individuals who had sought treatment and who had continued it, and the differences between the groups in treatment seeking and adherence. A total of 79% of those who were notified to seek medical care had done so. Antihypertensive drug therapy had been begun for 85% of these. After two years, 56% of those who had been found initially to be hypertensive and who were seen in the follow-up were still under treatment. In 43% of these the blood pressure was at the target level. No statistically significant differences in treatment seeking and adherence to it were found between the experimental and control groups, nor were differences found in the decline in the blood pressure or its target levels. Comparing with other studies shows, that results can be better if the health care system that carries out the screening procedure for hypertension also take active steps to bring the patient under treatment and keep him on the regimen.