In 490 working men, aged 40-59 years the sequelae of borderline arterial hypertension (BH) were evaluated. The patients with BH (n = 253) were matched with normal controls (n = 237). At 13 years the cardiovascular state, ability to work and mortality were assessed. A significantly more frequent incidence of left ventricular hypertrophy and overload was found when hypertension developed. In the group of initial BH less men continued work (36%) than in the control group (48.1%, p less than 0.01), despite the same age. A relation between the ability to work and blood pressure becomes more prominent while taking into account final diagnosis; i.e. 65.7% of actual normotensives, 56.4% of the patients with BH and 47.5% with hypertension continue their work. The mortality rate was higher (15.4%) in the group with BH than in the controls (8.4%, p less than 0.01). The highest death rate was found when BH was combined with other coronary risk factors. The results confirm the presence of both indirect (through the development of arterial hypertension) and harmful effects of BH. They also show the need of devoting special attention to patients with BH and concommitant coronary risk factors.