The authors investigated the effect of the ten-year intervention programme on the standard of detection, control and effectiveness of treatment of arterial hypertension in an industrial population. The prevalence of hypertension did not change during the investigation period (about 24%). In group B (1986) a decline of the blood pressure was recorded in all age groups on average by 10/0 mmHg (1.3/0 kPa) in men and by 15/9 mmHg (2/1.2 kPa) in women. In men detection improved and the ratio of treated hypertonics increased (p less than 0.05); in women the trend of improvement was not significant. The number of untreated subjects with hypertension did not change in the course of 10 years (15-16% of all hypertensive subjects). 50% hypertensive men and women were treated effectively in group A and 59% men with high blood pressure in group B; the ratio of effectively treated hypertonic women in group B did not change. There was no difference in the level of control of hypertension between men and women in either group. The differences in the prevalence and treatment of severe hypertonics (i.e. DPB greater than or equal to 110 mm Hg = 14.7 kPa) were not significant when comparing groups A and B (2.4% of group A and 4.1% of group B).